Two soluble protein fractions were found to increase under cold treatment in winter rape plants. They were the proteins of low molecular weight, impoverished in proline and methionine residues and localized in the citosol subcellular fractions. They seem to be linked in "situ" with the hydrophobic compounds of cytoplasm. Owing to those properties, they seem to be more resistant against salt-induced aggregation which may occur at freezing or at A01GP096.

Uridine incorporation into the shoot apex of the short-day plantChenopodium rubrum was investigated during a 16 h period of darkness and the following transfer to light. Uridine incorporation during this single inductive cycle was compared to incorporation under non-inductive conditions of continuous light. After transfer of the plants from light to darkness RNA synthesis was reduced to about half after the first two hours. This occurred not only when the plants were precultivated in continuous light but also after an interruption of the dark period by light for 31/2 h. The low level of uridine incorporation was maintained for the whole duration of the dark period. Incorporation regained its initial level after exposure of the plants to light irrespective of the duration of the preceding dark period. After this immediate rise of uridine incorporation in plants transferred from darkness to light a slight temporary decrease was observed in light. In darkness the decrease of incorporation into the nucleoli was still more marked than the reduction of overall incorporation. After the termination of the dark period incorporation into the nucleolus rose slowly and extranucleolar incorporation was relatively enhanced during the first 10 h of light in induced plants. The fluctuations of RNA synthesis observed in the shoot apex during photoperiodic treatment may be regarded as a necessary condition for the transition from the vegetative to the reproductive state.

The content of endogenous auxins was examined in apical buds ofChenopodium rubrum plants induced by a photoperiodic cycle of 16h darkness and 8h light followed by a dark period of various duration so as to correspond with either maximal or minimal flowering response in the endogenous rhythm in capacity to flower initiated by the photoperiodic treatment. Apical buds of potentially generative plants contained less auxins than apical buds of plants which remained in the vegetative state. Apical buds from plants treated with kinetin (1. 10^-3 M) and therefore remaining in the vegetative state showed an auxin level comparable to that of untreated plants exhibiting minimal flowering response irrespective of the duration of the second dark period. Plants cultivated on a sucrose solution (0.6 M) during the second dark period became generative even at the normal minimum of flowering. The auxin content of the apical buds was low, similarly as in untreated plants induced for a period leading to maximal flowering response. On the other hand, apical buds from plants grown on sucrose solution during a dark period leading to the manifestation of maximal flowering response showed a relatively high auxin content comparable to that found in untreated plants which had obtained a more extended induction by three photoperiodic cycles. The results are discussed with respect to the possible role of endogenous auxins in the regulation of the changes in growth correlations occurring in the shoot apex during photoperiodic induction and in the expression of the competence to flower.

Applications of various amounts of GA₃ onto the shoot apex of biennial rosette-plantHyoscyamus niger L., exposed to long days and non vernalized, caused internodes formation and stem elongation. The stem length was proportional to the amount of GA₃ applied. Number and length of developed internodes and the whole length of the shoot were maximal in plants treated with a greater amount of GA₃. In the end, stem elongation stopped and plants formed perchedrosettes without flowering. Hence, gibberellic acid participates in mechanisms of flowering only by indirect effect on stem elongation and not directly on flower formation itself.

Kinetin at a concentration from 3.10^-6 M to 1.10^-3 M was applied to the plumule ofChenopodium rubrum plants during photoperiodic induction. Different levels of induction were compared (one and three short days). The higher concentrations of kinetin applied to induced plants inhibited flower formation. The rate of leaf initiation was increased under these treatments. Lower concentrations of kinetin (from 3.10^-6 M to 1.10^-5 M) usually promoted lateral bud formation and flowering. The step-wise application of kinetin revealed that the inhibitory effect on flowering had been restricted to the inductive period.
The effects of kinetin, benzyladenine and trans-zeatin were compared in plants partially induced by two short days. High concentrations always inhibited flowering. Benzyladenine was the most effective in this respect.
Root removal diminished the inhibitory effects of cytokinins on flowering as was stated with benzyladenine.
It is assumed that endogenous cytokinins play a role in the regulation of organogenetic activity of the stem apical meristem. Depending on the photoperiodic conditions, they presumably exert their activity by maintaining the vegetative functions of the apex.

The nucleic acid fractions obtained by chromatography on MAK columns were compared in 4 variants ofChenopodium rubrum plants treated in different ways during floral induction. The first variant was normally induced to flowering. The second one was inhibited by application of FUDR to the apical bud on the third day of induction. In the third variant the inhibitory effect of FUDR was reversed by application of THY 24 h after FUDR treatment. In the fourth variant THY was applied 24 h after the termination of induction at a time when it was no longer able to reverse the inhibition of flowering. In plants treated with FUDR, a decrease in DNA and RNA synthesis was observed. After reversal of the inhibitory effect of FUDR by THY, DNA synthesis remained somewhat lower than in the control variant but RNA synthesis reached the same level as in the controls or even surpassed it. In plants to which THY was applied at a time when it was no longer possible to reverse flowering, the results obtained from different experiments were not identical. In some experiments nucleic acid synthesis remained lower than in the variant in which THY restituted flowering. In other experiments nucleic acid synthesis was fully restituted and reached the same level as in the control variant. This phenomenon is explained by the different size of the experimental plants at the beginning of the different experiments. The results are discussed with respect to the relation of the dynamics of nucleic acids to growth and development of the plants.

Studying the spread of mycoplasma, the causal agent of potato witches' broom disease, in tomato plants after grafting with infectious grafts ofNicotiana glaucaGrah., we found that after 9 days of graft symbiosis a hundred per cent infection occurred, whereas with infectious grafts ofSolanum lycopersicum this took place after 16 days. The first symptoms of the disease were manifested on tomato plants 21 days after grafting with infectiousNicotiana glauca grafts and 28 days after grafting with infectious tomato grafts. The results obtained present evidence for the possible preference of tomato plants for mycoplasma.

The fruit pitting symptoms on cherries, plums and prunes were investigated from the standpoint of their etiology. Tomato bushy stunt virus (TBSV) was isolated from pitted fruits of these plants and from their leaves and identified by means of biological and serological methods. Both isolates reacted with antisera againstPetunia and artichoke strain of this virus. In addition, the etiology of pseudopox disease of plum and that of cherry detrimental canker is discussed.

The paper gives more detailed characteristics of Arabis mosaic virus (AMV) and tomato bushy stunt virus (TBSV) isolated from lilac, the latter being identified in lilac (from plants suffering from yellow ring disease) for the first time. The isolate of TBSV from lilac, from which an antiserum with a titre of 1024 was prepared, is closely related to the artichoke strain. Information is given about two types of ringspot disease and about chlorotic ringspot of lilac. Whereas in the leaves of lilac suffering from ringspot disease (of ring mosaic type) the presence of AMV was demonstrated, the sap transmission from the leaves diseased with ringspot of linepattern (and wave-like mosaic) type failed; from the leaves affected by chlorotic ringspot a mixture of AMV and cherry leaf roll virus was identified. In addition, the polyetiological nature of "spring" mosaic and necrotic mosaic of lilac, in which bacteriumPseudomonas syringaevan Hall, was found is dealt with. The TBSV was also identified in the isolate of necrotic mosaic.Additional index words: Lilac ringspot, chlorotic ringspot, yellow ring, "spring" mosaic, necrotic mosaic, cherry leaf roll virus,Pseudomonas syringaevan Hall.

The influence of gibberellic acid (GA³) and kinetin (6-furfurylaminopurine) on the regeneration ability of the basal and apical thallus fragments ofFucus vesiculosus L. was examined. The naturally occurring gibberellin and kinetin-like substances in these thallus fragments were also studied. It was found that exogenously applied GA³ markedly increased the number of adventitious branches formed on the cut surface of the thallus fragments taken from the apical parts of plants. The concentration of 0.001 mg GA³ I-1 proved to be the most effective. The growth promoting effect of GA³ was increased by simultaneous action with kinetin. In experiments in which the fragments of the basal parts of the thallus were treated with GA³, as a rule a slight growth inhibition was observed. The growth responses of the investigated plant tissues to gibberellin and kinetin varied according to season. Usually their susceptibility to the applied plant hormones was greater in spring than is summer. The shifts in growth reaction were related to the seasonal changes in the content of endogenous gibberellin and kinetin-like substances in the investigated parts of the thallus. It is suggested that growth regulators of the gibberellin and cytokinin type are involved in the regeneration processes inFucus.

In controlled environment growth chambers, the effects of foliar and root applications of 2-chloroethyltrimethylammonium chloride (CCC) and 2,4-dichlorobenzyltributylphosphonium chloride (Phosfon) on the translocation of³²P fed to leaves, were investigated. When applied to leaves or to root, CCC had no effect on the relative amounts of³²P radioactivity retained by the fed leaf 5, 20 and 80 h after feeding. At 20 and 80 h after feeding, Phosfon concentrations of 0.01 and 0.1mg l^-1 reduced retention of the applied³²P. 80 h after³²P feeding, CCC concentration of 1 mg l^-1 applied as a foliar spray or to the root enhanced the downward movement of³²P. Phosfon at low concentrations, particularly at 0.1 mg l^-1, on the other hand, favoured an upward transport of the applied³²P. Foliar applications of CCC and Phosfon at high concentrations had no significant effect on³²P transport to the root and the shoot below the fed leaf, while root applications of CCC and of Phosfon inhibited downward transport. Root applications generally caused greater alterations in³²P distribution patterns than did foliar applications. On the basis of total active ingredient uptake, Phosfon was more effective than CCC in altering translocation patterns.

Callus tissues were derived from the stem of healthy tomato plants (Lycopersicum esculentumMill. ev. Průhonické) and of plants infected with potato witches' broom-a disease caused by mycoplasma. Callus cultures were established on modified fully synthetic media described byMorel (1948) and byMurashige andSkoog (1962). Callus cultures obtained from diseased plants were grown and subcultured on both media, growth in primary isolates from healthy plants took place on the Murashige and Skoog medium only. Growth of callus tissue derived from diseased plants was more vigorous even after several subcultivations in comparison with callus tissues isolated from healthy plants. Variations in the morphology in these callus cultures were not noted. Callus cells of diseased plants varied in size; they were about 50% larger than those from healthy ones. Implantation of primary and subcultivated callus tissues into tomato stems of healthy plants did not show any symptoms of infection on test plants.

Big vein disease occurring on lettuce plants cv. 'Pražan' was identified and the susceptibility to this disease was tested on 9 lettuce cultivars of foreign origin. Lettuce big vein virus was confirmed to be the cause of the disease. The transmission of the LBVV by the fungusOlpidium brassicae (Wor.)Dang., the sporangia of which were found by microscopy in the cells of surface tissues of lettuce roots, was experimentally proved. Rod-like particles, the average length of which was estimated at 244 nm, were found in the roots of diseased plants. LBW transmission by mechanical inoculation and by aphids could not be proved.

The effect of short and long term auxin treatments on the elongation of axillary buds and³²P accumulation were studied in 2-leaf decapitated Alaska pea sailings. It was found that (1) auxin delayed the elongation of the lateral buds, (2) none of the auxin concentration applied completely inhibited the elongation of axillary buds, (3) auxin had no retarding effect on the growing buds, (4) strong polarization of 32P occurred in the parts above the treated leaf, when auxin was applied for a short period just after decapitation, (5) long term auxin treatments did not induce any such polarization of 32P to the parts above the treated leaf, (6) the root acted as an alternate accumulating organ for 32P when the apex was removed and the buds were inhibited, and (7) in decapitated plants the growing buds polarized 32P.

The effect of 2,4 dinitrophenol and increased viscosity of the absorption solution on the absorption of phosphorus by excised roots of maize plants was investigated. The concentration of the solution was 0.1 mM KH₂PO₄, the activity of³²P was 52 µCi l^-1. The temperature of the absorption solution was 26 °C, pH 5.5, aeration prior to the experiment. There was 11 of solution for every 1 g of roots. Two basic variants were used for comparison: with non-flowing solution and with solution flow (circulation) of 0.162 cm s^-1, respectively. In all cases, 2,4 dinitrophenol reduced the rate of phosphorus absorption by the roots regardless of the mechanism of phosphorus supply to the roots (diffusion, mass flow). If it is proved that 2,4 dinitrophenol inhibits the active uptake of phosphorus, then the uptake of phosphorus by the roots increased under the influence of mass flow will be active,i.e., connected with energy metabolism.
Raising the viscosity of the absorption solution 3.3 times over that of water by means of potato starch substantially reduced the absorption of the phosphorus transported to the absorption zone by diffusion and practically did not affect the rate of absorption, or the amount of anions transported to the absorption area by mass flow.

Uridine-³H incorporation and RNA concentration were investigated in different parts of the shoot apical meristem ofChenopodium rubrum using autoradiography and cytophotometry. A single inductive cycle was sufficient to bring about postinductive first events in the shoot apex but not for complete flower differentiation. The initial activation of RNA synthesis manifested itself in all zones of the apex. The first increase was more conspicuous in the peripheral than in the central zone. The indications of the first events in the apices after a single inductive cycle disappear prior to morphological reversal to the vegetative state. Induction by three short days led to rapid flower differentiation. The increase in RNA synthesis and concentration was most conspicuous in the central zone in this case. The ratio of RNA synthesis and content between bud and leaf primordia (B/L) also change in relation to photoperiodic induction. In vegetative plants the B/L ratio was low while after induction it increased.
The shifts in activity of RNA synthesis observed in the shoot apical meristem are related to the changes in growth activity of the different parts of the apex. The growth ratios in the apices bear the character of growth correlations. The change in the growth correlations following photoperiodic induction together with the total activation of RNA synthesis are considered to represent one of the first events of the transition to the reproductive state.

Behaviour of CMV, PVY and BYV was investigated in serological precipitin drop as well as gel diffusion reactions using crude extracts from infected plants and antisera against intact viruses. Gel diffusion reaction of PVY was positively influenced by degradation of viral particles with pyrrolidin while gel tests with CMV and BYV were influenced negatively. Antiserum and antigen titers of CMV, as determined in gel diffusion tests, were 4 to 8 times higher than in drop tests. The titer of PVY antigen, as determined in gel diffusion test, was the same as in drop test. Finally the titer of BYV antigen was 16 times lower in the Ouchterlony tests. On the basis of the ascertained differences in the behaviour of PVY and BYV the pyrrolidin degradation may be recommended for PVY but not for BYV. Diagnosis of PVY or BYV by testing crude extracts from infective sources for the presence of soluble antigen is not successful for the time being.

Suitable conditions for the fertilizationin vitro in maize have been studied. The germinating capacity of pollen in synthetic media was low; it was confirmed that it might be stimulated by supplementing agar with egg yolk. Application of pollen onto styles overhanging from the culture medium of excised ovaries was examined. After 5 days the styles could be cut off the ovaries, for the pollen tubes had already penetrated the embryo sacs. However, better results were obtained when cultivating ovaries along with segments of the maize cob. Solid media were more suitable for the development of kernels. Some of them germinatedin situ and gave rise to normal plants. From nucellar meristems of young kernels a callus could be derived which, on further cultivation, became green and regenerated shoots and roots. The cells of meristems exhibited a varying number of chromosomes.

Flowering ofChenopodium rubrum seedlings fed different sugars at a concentration of 0.6 and 0.4 M, reap, during a single inductive cycle was stimulated or inhibited in dependence on the conditions of germination and initial growth. Plants allowed to germinate at alternating temperatures of 28 °C and 5 °C showed a slower initial growth and their development was stimulated by some sugars as compared to controls induced in the absence of sugars. Plants germinated at alternating temperatures of 32 °C and 5 °C exhibited a rapid initial growth and flowering was inhibited after induction in the presence of sugars. On the other hand, development proceeded more rapidly in control plants induced in the absence of sugars after germination at the higher temperature than after germination at the lower one. The differences between the two variants quoted above could be observed also after induction by two 16 h dark cycles. Glucose and sucrose were most effective in stimulating flowering under appropriate conditions of germination. Fructose was less effective and the action of maltose was very weak. Xylose, ribose and galactose were innocuous, while arabinose, glucoso-6-phosphate and mannitol were toxic to the plants. The sugars inhibited root growth in all cases and led to an increase in starch accumulation in the underground and overground plant organs. At a concentration of 0.6 M they mostly inhibited the length of the cotyledons and, especially, of the first leaf; at a concentration of 0.4 M growth of the overground organs was stimulated. The results are discussed with respect to the possible ohanges in photoperiodic sensitivity brought about by the rate of initial growth.

Irradiation of the seeds of radioresistant kohlrabi with gamma-rays causes at doses SO to 300 kR a decrease in growth and a drop in tryptophan (Try) level in seven-day-old plants. The level of glucobrassicin (GLUBR), 3-indolylacetonitrile (IAN) and gibberellic acid (GA3) in these plants increases up to a maximum with a dose of about 150-200 kR, afterwards it decreases. We assume that the specific system of auxin synthesis inBrassicaceae plants takes an important part in the reparation processes and thus in the radioresistance of these plants as well. In contrast to the divergent systems of auxin biosynthesis in other plants which are damaged by lower doses of irradiation, the specific system of auxin formation via GLUBR synthesis, under formation of IAN intermediate, is widely not. attacked by radiation. Thus, these irradiated plants are supplied with auxins and with gibberellins too, the both hormones having a radioprotective effect.

A thin layer of homologous antiserum (against the beet yellows virus - BYV) between the leaf surface and a Parafilm membrane totally inhibited the acquisition of BYV by aphidsMyzus persicae (Sulz.), but it did not affect the inoculation of BYV by infective aphids. BYV transmission decreased with aphids picking up the virus from leaves coated with a normal rabbit serum. Aphids sucking on purified BYV suspension through the Parafilm membrane as well as aphids allowed to probe into leaves of healthy plants spread with an infectious purified BYV suspension failed to transmit BYV. No BYV particles could be detected in eluates from stylets and labia cut off from aphids which had probed on BYV infected plants by electron microscopic examination. The acquisition seems to be the most important phase for the aphid transmission of BYV which is apparently carried on the stylet surface.

Five different isolates of beet yellows virus were maintained without any changes in their properties onTetragonia expansaMurr. syn.T. tetragonoidesPall. for a long period of time. According to their characteristics and different properties especially in a diploid inbred line of sugar beet the isolates are considered to be strains of BYV and are classified into three groups: group of mild strains (the mild masked and mild strains), normal strains (the common strain) and necrotic strains (the severe necrotic and necrotic strains). The necrotic strains of BYV were relatively easily transmissible manually to sugar beet plants and other indicator species. The common strain can be transmitted to sugar beet,Chenopodium quinoaWilld. but not toC. capitatumL. Asch. Mild strains are transmissible with difficulty andC. quinoa is the only species which develops a larger number of local lesions after inoculation. In contrast to the mild masked and common strains it is manually transmissible toC. capitatum. The mild masked strain can not be transmitted to sugar beet.Nicotiana quadrivalvisPursh. is not susceptible to mechanical inoculation with BYV. Aphid transmission withMyzus persicae (Sulz.) was positive in experiments with necrotic strains only. Mechanical transmission of BYV was successful also toC. foliosum(Moench) Asch.,C. murale L. andClaytonia perfoliataDonn. The last two species were susceptible to inoculation by aphids as well. Attempts to transmit the virus manually toT. expansaMurr. andC. giganteumDonn. failed.

Total activities of nitrate and nitrite reductases were higher in 4 to 20 day old maize plants in the leaves than in the roots. The ratio of activities found in the leaves and in the roots respectively was much higher in the case of nitrate reductase than in the case of nitrite reductase. On the other hand higher glutamate dehydrogenase activity in the roots than in the leaves clearly indicates that the roots play a more important role in the assimilation of ammonium than in the assimilation of nitrate. When comparing the distribution of seminal and nodal adventitious roots of maize seedlings with the assimilation of inorganic nitrogen on the basis of enzyme levels, it could be deduced that during the first 20 days of seedling growth seminal roots were more involved in the assimilation of nitrate whereas nodal adventitious roots were more active in ammonium assimilation.

Plants ofPlectranthus fructicosus were grown in two controlled environments -"spring" and "summer" conditions - differing in temperature and air humidity (day/night 20/15 and 27/22 °C; 80/98 and 50/80 % relative humidity) in order to study the influence of environmental conditions on the development of photosynthetic characteristics of individual leaves. The contribution of individual leaves to plant photosynthesis was very similar in both environments, the maximum shifting from bottom leaves to leaves of middle insertion levels during plant ontogenesis. On integrating the values of leaf photosynthesis for the whole vegetation period, the 5th leaf in "spring" conditions and the 4th leaf in "summer" conditions showed the highest contribution to plant photosynthesis (29 % resp. 25% of total net CO₂ influx). The "photosynthetically mature" leaves of middle insertion levels played the main role in CO₂ uptake of whole plant.

When examining plants of white mustard (Sinapis alba L.), a significant relationship between the size of the roots and the yield was found, both in a pot experiment and in a field one. The yield was influenced by the size of the root system during and after flowering time. Especially the number of seeds has increased, and the average weight of seeds showed the same tendencies after the flowering time. The productivity of plants with an above-average yield was increasing more quickly than the size of their root system. From the beginning of the vegetation till the end of flowering these most efficient plants showed the lowest permitivity dispersion and the highest dispersion after the flowering time. The dispersion has increased towards the end of vegetation.

Pea plants grown in nutrient solution in which K⁺ ions were equimolarly replaced with Na⁺, NH₄⁺ or Rb⁺ did not show morphological symptoms of potassium-deficiency. The activity of diamine oxidase in these plants was higher than in controls. Similarly higher diamine oxidase activity was found in plants grown in a complete nutrient solution supplemented with putrescine.

Physiological effects of volatile substances released by the overground as well as by the underground organs of higher plants were studied. The activity of the volatile substances was tested both when these substances were allowed to act directly in the air and when they were dissolved in water in the form of solutions. Plants which do not contain essential oils or which are not rich in them as well as those abounding in essential oils and other volatiles were used in the experiments. The physiological activity of the volatile substances was tested on rye seedlings.
The overground as well as underground mature organs of the tested plants were found to release volatile substances causing, when acting directly, in the majority of cases an inhibition of the growth in length and of the formation of dry matter in rye seedlings. A pronounced inhibition of the growth of rye seedlings was brought about especially by the volatile substances of "aromatic" plants such as common dill, wild thyme, yarrow milfoil, garden thyme, marjoram, etc. The volatile substances released by the organs of "non-aromatic" plants like sugar-beet, common sunflower, quackgrass, etc., were found to bring about a significant inhibition of the growth of rye seedlings, too.
The volatile substances released by the plant organs were found to be altogether absorbable in water and physiologically active also in the form of water solutions. With the exception of volatile substances from hemp and quackgrass leaves, which brought about a mild stimulation of the dry matter formation in rye seedlings, inhibitory effects of these solutions were found to prevail in all cases. Most effective were the solutions of the volatiles from some of the "aromatic plants".
An assay for olefines in the atmosphere of the experimental vessels demonstrated that in almost all cases ethylene is being released by the plant organs.

In Vietnam a green strain of tobacco mosaic virus was isolated having TIP 89°C (10 min) and causing systemic necrosis in tobacoo 'Xanthi-nc' and sometimes also inDatura stramonium. In symptomless tomato plants an elongated virus belonging apparently to the Carlavirus group (NL 630 nm) was found. In papaya trees showing severe symptoms of mosaic and/or ringspot elongated virus particles (NL 730 nm) were observed; this virus being apparently a member of the Potyvirus group, resembled as far as its symptoms in papaya are concerned, the papaya ringspot or the distortion ringspot. In Cambodia some young rubber trees showed malformed leaves (esp. edges and veins) with yellow discolorations along the veins. Such leaves contained elongated virus-like particles (rigid or slightly flexible) of various length (60 to 880 nm), so that their normal length (NL) could not be established precisely. Particles 120 to 150 nm long occurred very frequently.

In cotyledons ofChenopodium rubrum L. polydisperse RNA is synthesized in the region of the low molecular weight RNAs during photoperiodic induction. After short-time labelling the rate of 4s RNA synthesis was always higher in induced plants than in plants having obtained a light-break in the middle of the dark period. When glucose was added to the nutrient medium during the dark period of a single photoperiodic cycle the rate of nucleic acid (NA) synthesis was higher in non-induced plants than in induced ones at the termination of the dark period. In plants induced by two cycles in the absence of glucose the rate of NA synthesis at the termination of the second dark period was higher in induced than in non-induced plants. This difference is due to the differential kinetics of NA synthesis during darkness. In plants induced in the presence of glucose the peak of the rhythm in NA synthesis was advanced by 4 h relative to that found in plants induced in the absence of sugar. Thus, the termination of the dark period coincided with the negative slope of the oscillation in plants induced in the presence of glucose, while in plants having obtained a light-break NA synthesis decreased only slightly after having attained its peak. In plants induced in the absence of glucose the termination of the dark period coincided with the peak in the rhythm in NA synthesis. The rhythm in NA synthesis of the cotyledons during the dark period of an inductive cycle is out of phase with the rhythm in flower initiation.