Roberts and Struckmeyer — 99 — Anat. and Histol. Changes 



Relation with Vernalization : — A comparable situation exists in 

 connection with any possible relation of vernalization and anatomical de- 

 velopment. If vernalization be given a narrow definition, as a cold treat- 

 ment, or if it be given a wide meaning, as any blossom-inducing treatment 

 even including photoperiod as one item, it would not have a consistent 

 relation with anatomy as no one factor of the external environment as 

 moisture, nutrient, grafting, girdling, temperature, etc., have the same 

 effect upon the inducing of sexual reproduction of different types of plants. 

 Flowering is, however, correlated with anatomical development. 



It would be interesting to know whether there are anatomical changes 

 in the plants exhibiting devernalization comparable to those found in plants 

 which do not have persisting after-affects (34). 



Relation with Phasic Development: — The relation which has been 



found to be consistent between anatomical changes and the start of the 

 cycle of sexual reproduction (blossom induction) should be a means by 

 which to measure the general applicability of the proposition that the plant 

 comes to flower by a series of phases, each of which must be completed 

 before a succeeding one is entered. 



Some interesting materials for study would be: 



1. Pigweed (Amaranthus retroflexus) seedlings which flower with the first pair 

 of leaves and even prior to the differentiation of secondary tissues, when grown in 

 warm, short days. 



2. The quick change from a non-flowering to a flowering state of Xanthium 

 after two long-nights (staminate blossoms may be induced by only one long dark 

 period). 



3. Reversion to the vegetative condition of terminally flowering types of plants 

 following a change of environment. (Rather spectacular examples can be produced 

 with such plants as beets [Beta vulgaris] as the stems thicken into "beets" when the 

 plants are transferred to an environment unfavorable to flowering.) 



4. The continued flowering of plants with a systemic flowering habit after com- 

 plete induction although having been moved into an environment unfavorable to in- 

 duction. 



5. Plants like Nicandra physalodes and buckwheat (Fagopyrum esculentum) 

 which start to flower under very wide extremes of environmental condition and con- 

 tinue to grow and initiate and develop flowers even after maturing fruits are present 

 on the plants. 



It is suggested that observation of the anatomical conditions in the plant 

 might be an aid in determining the boundary between the vegetative and re- 

 productive phases. There is a relatively long lapse of time in many plants 

 between the start of induction and the appearance of even microscopic 

 blossom primordia. (Observation of the cambial condition in petioles can 

 be made without greatly modifying a plant for later observation.) 



Comment : — Use of the techniques of photoperiodic and vernalization 

 experiments does not appear to offer solutions of the problem of sexual re- 

 production. The manipulation of external factors gives a record of the 

 treatment needed to initiate sexual reproduction and thus serves as an aid 

 in the control of plants for commercial or experimental purposes. An 

 understanding of the physiological processes of reproduction would appear 

 to depend upon a study of the internal factors and mechanisms involved 



