Vernalization and Photoperiodism — 96 — A Symposium 



nights are cold (55°F) and which also appear in the fields of the Mid- 

 western United States of America as what farmers call "duds" (36). 



A detailed study of the anatomy of this type of plant shows definitely 

 that the large diameter is due to increase in parenchyma cell size and not 

 to increased xylem formation from cambial activity (Fig. 9). The thick- 

 ness of these stems and presumably also of the short day plants of Psarev, 

 is due to a combination of low temperature and short days and is not asso- 

 ciated with induction. Plants which fruit normally in short days and warm 

 night temperatures remain slender. Also, they have the anatomical condi- 

 tions typical of reproductive plants (Figs. 10, 11). More evidence is 

 needed on the relation of anatomical condition and reproduction. This 

 should be secured by sampling and studying plants at the time of induction 

 and early blossoming in comparison with actual non-flowering plants. 



WiTHROW (40) has found an anatomical condition in non-flowering 

 and flowering plants like that described by Wilton and by Struckmeyer. 

 This consisted of reduced cambial activity and limited phloem formation 

 in plants which flowered. This was found to be true of both long- or short- 

 day plants and also occurred without regard to the nitrogen nutrition. 



Plant Differences : — In the course of the induction of blossoming by 

 numerous methods to ascertain the consistency of anatomical history of 

 sexual reproduction, a particularly interesting difference in the reaction of 

 plant species has been observed. We do not refer to the different or even 

 opposite flowering responses of different species to like photoperiods or 

 temperature treatments or age but to another plant characteristic which 

 appears to have as much effect upon the type of experimental evidence 

 which is secured as does the influence of certain external conditions. We 

 refer to the blossoming habit : Plants which have only terminal blossoms 

 react differently from those which have blossoms at numerous growing 

 points along the stem; i.e. those which flower systemically (29). Thus 

 Garner and Allard (5) showed there was no transfer of the flowering 

 stimulus between branches of Klondyke cosmos (Cosmos sulphureus) , a 

 terminal flowering species. At much later dates morning glory (Ipomoea 

 purpurea var. Heavenly Blue) (27), Xanthium (7), soybean (Glycine 

 max) (1) and other plants with a systemic flowering habit were reported 

 to show a transfer of the flowering stimulus. 



This relation of terminal and systemic flowering habits to reaction to 

 flowering stimulus from donor branches or leaves has been checked in only 

 a few score of plants. It is anticipated that an exception to the general 

 classification may be found. The nearest to it to date is Perilla jrutescens 

 (nankinensis) . No transfer of the flowering stimulus with this systemic 

 flowering plant has been secured in our trials even when the leaves are 

 removed from the receptor branches. In the experience of some workers 

 it is also necessary to keep the flowers removed from the donor portion. 

 We have not tried this technique. 



It is also interesting that plants flowering terminally are not induced to 

 blossom by grafting the stem of a flowering plant onto a non-flowering one. 

 (It would be interesting to know what the results of Moshkov (4, p. 230-1) 

 would have been had he "decapitated" the receptor tobacco plants at a 

 lower level, that is, in a region of the stem where blossoms do not ordinarily 



