Permanence and Location of the Induced State • 83 



tion of the transmission, by grafting or otherwise, of a stimulus 

 resulting from vernalization alone rather than vernalization fol- 

 lowed by long days; such a demonstration would be necessary to 

 establish the existence of vernalin. 



In the course of work on Kalanchoe, Harder (1948) concluded 

 that short-day treatment caused the production not only of flower- 

 ing hormones but also of "metaplasin," a substance responsible for 

 the large and easily measured changes in vegetative habit (par- 

 ticularly leaf succulence) accompanying flowering. Studies on its 

 transport, analogous to those on the floral hormones in Kalanchoe, 

 did not permit any separation of one from the other. The entire 

 evidence for the existence of metaplasin as a separate entity is this: 

 subjecting the upper portion of a plant on short days to a prolonged 

 chloroform treatment that will strongly inhibit flowering has no 

 influence on the vegetative effects of the photoperiod. This is 

 hardly unequivocal proof that short days result in the production 

 of two different substances, one specific for flowering and one for 

 the vegetative changes. It is equally reasonable to assume that the 

 processes leading to flowering are in some way different and more 

 sensitive to this inhibition than those controlling vegetative growth, 

 but it does not follow that the initiating conditions or substance 

 brought about by photoperiodic treatment is necessarily multiple. 



If the conclusion at present must be that vernalin and meta- 

 plasin may be myths, they nevertheless serve a purpose here. They 

 remind us, to whom these particular errors may seem obvious, that 

 the difficulties of analyzing the responses of complex organisms, 

 coupled with the desire to achieve simple interpretations, may lead 

 even some foremost investigators astray. 



PERMANENCE AND LOCATION OF THE 

 INDUCED STATE 



As indicated in the preceding chapters, the effect of a par- 

 ticular treatment, temperature or photoperiodic, may persist and 

 be expressed in flowering response later, even though no anatomical 

 changes are evident when the treatment is stopped. Induction, as 

 this aftereffect is called, is widespread though not universal, and 

 differs considerably in both permanence and location within the 

 plant. Confining this discussion first to the photoperiodically in- 



