376 SENESCENCE AND REJUVENESCENCE 



phytoids are concerned and that each period represents the life 

 history of a generation of phytoids. The life of the perennial, 

 multiaxial plant is not comparable to the life of an individual 

 animal, but is made up of innumerable life cycles with senescence 

 and death of the more highly differentiated parts in each generation. 



From this standpoint the cases of premature flowering are to be 

 regarded simply as cases of prematurely established physiological 

 conditions resembling those which usually arise only after a con- 

 siderable period of vegetative activity. It is impossible to con- 

 sider these cases at length, and in many of them the determining 

 conditions have not been analyzed. One interesting case recently 

 recorded by Doposcheg-Uhlar ('12) may, however, be mentioned. 

 Bulbs of a species of Begonia could be made to produce either a 

 vegetative shoot or an inflorescence at once according as they were 

 allowed to produce roots or not. The roots provided for the 

 entrance of water and salts and so made possible the transforma- 

 tion of the organic reserves in the bulb into protoplasm, and under 

 these conditions complete rejuvenescence to the vegetative con- 

 dition was possible. When, however, root formation did not occur, 

 the metabolic conditions in the cells were those characteristic of an 

 advanced stage of the life cycle under ordinary conditions and 

 growth from the bulb resulted in the immediate development of 

 the highly differentiated flower structure. The early flowering of 

 various other plant species grown from bulbs is probably to be 

 interpreted in the same way. The internal conditions in such cases 

 are those of relatively advanced age. 



Numerous cases of the transformation of an inflorescence, a 

 flower or some part of a flower, into a new vegetative axis have 

 been recorded by various authors (see pp. 246-47), and Klebs, 

 Goebel, and others have induced this transformation by subjecting 

 the young inflorescence or flower to external conditions favorable 

 to vegetative growth.' As Goebel ('08, pp. 11 7-18) suggests, 

 these cases are undoubtedly to be interpreted as cases of return to 

 a juvenile stage. The external conditions have made dedifferen- 

 tiation and rejuvenescence possible, even in the relatively highly 

 differentiated flower. 



' See the references given on p. 246, and particularly Klebs,'o3, '06. 



