374 SENESCENCE AND REJUVENESCENCE 



accumulation of inactive or relatively inactive organic substances 

 in the cells and consequently a decrease in metabolic rate. We see 

 also that such internal conditions bring about a higher degree of 

 differentiation in the plant than the conditions accompanying 

 vegetative growth. Moreover, the parts particularly involved in 

 this differentiation — the inflorescence axis or the flower — do not 

 under the usual conditions undergo any further vegetative growth, 

 but, after their development is completed, die a natural death, 

 and in many cases this natural death involves the whole plant, 

 the seeds only remaining alive. 



The evidence seems then to point very clearly to the conclusion 

 that flowering in the plant is characteristic of an advanced stage 

 in the hfe cycle — that the blooming plant is physiologically rela- 

 tively old. The conditions which prevent flowering and favor 

 vegetative growth are simply such as keep the plant in a relatively 

 young condition by preventing the accumulation of the organic 

 substances and bringing about repeated vegetative reproduction 

 in consequence of growth. 



It may seem at first glance that the metabolic conditions in the 

 flower are not in accord with the conclusion that the flower is the 

 product of advanced age in the plant. The flower, particularly in 

 its earher stages, is usually the seat of a very intense respiratory 

 activity and often possesses a higher rate of oxidation than any 

 other part of the plant.' If blooming is a feature of advanced age 

 and if rate of oxidation is in any way associated with age, it would 

 seem that we ought to find a low rate of oxidation in the flower. 

 Such a conclusion, however, ignores completely the fact that the 

 formation of the flower is a complex reproductive process and 

 unquestionably involves a greater or less degree of rejuvenescence 

 which appears in increased respiratory activity, and that in the 

 formation of the pollen grains in the anther and the ovules and 

 embryo sacs in the ovary extensive reproduction again occurs. 

 Moreover, in the developing flower the proportion of actively grow- 

 ing cells to the total weight is greater than in the vegetative por- 

 tions of the plant, with the exception of the embryonic growing 



'See A. Maige, '06, '07; G. Maige, '09, '11, and, for further references, Pfeffer, 

 '97; Nicolas, '09. 



