CONDITIONS OF GAMETE FORMATION 373 



1. In bright light with active photosynthesis and intense absorption of 

 water and salts active vegetative growth results. 



2. In bright light with active photosynthesis but with limited absorption 

 of water and salts profuse flowering results. 



3. With a medium water and salt absorption the intensity of photosyn- 

 thesis determines whether vegetative growth or flowering shall occur. When 

 the production of organic substance is decreased, e.g., in blue light, vegetative 

 growth results, and when it is increased, flowering occurs.' 



These results have in general been confirmed by the observations 

 and experiments of others, so that it seems to be a well-established 

 fact that the development of flowers depends upon different meta- 

 bolic conditions from those which determine vegetative growth. 

 Observation and experiment agree, moreover, in indicating that 

 flowering is determined by the accumulation in the plant of organic 

 substances which, because of insufficiency of water and salts, are 

 not completely transformed into metaboKcally active protoplasm 

 or its products, and so do not simply produce growth, but rather 

 a change in metabolic conditions in the direction of differentiation 

 and senescence. 



If the formation of a new vegetative tip, i.e., a new vegetative 

 axis, is the generalized form of reproduction in the flowering plant 

 (cf. pp. 238-39), then there can be no doubt that the flowering is a 

 specialized type of reproduction. The flower certainly shows a 

 much higher degree of differentiation of its parts than does the 

 vegetative axis. Moreover, the metabolic conditions which favor 

 flowering are conditions which cannot arise at once in a plant indi- 

 vidual beginning its development and dependent upon external 

 sources of nutrition. At least certain stages of metaboHc history 

 must be passed through before the plant is capable of being brought 

 into the flowering condition. Authorities in general agree that a 

 certain amount of vegetative growth must occur before the plant 

 can be induced to bloom. In other words, the plant must appar- 

 ently attain a certain stage of development, a certain physiological 

 age, before flowering is possible. But this stage having been 

 attained, the further metabolic conditions which favor flowering 

 are similar in character to those which bring about morphological 

 differentiation and senescence in animals, for they consist in the 



' Klebs, '06, pp. 105-6. 



