372 SENESCENCE AND REJUVENESCENCE 



an early stage, and instead of flowers axillary buds become active 

 and grow out into vegetative branches and the inflorescence is 

 transformed into a vegetative complex and the formation of gametes 

 does not occur. It should be noted that in this case it is only the 

 later stages of flower development which are inhibited by the low 

 light intensity. The specialization or change, of whatever character 

 it may be, which determines the development of an inflorescence 

 has occurred in these plants, but it stops at a certain stage and with 

 its cessation new vegetative individuals arise in consequence of 

 physiological isolation, and the vegetative hfe is resmned. 



Klebs records similar results for various species and states that 

 in all plants which do not possess a considerable volume of reserves 

 a decrease in illumination suppresses the formation of flowers. 

 According to Klebs, this influence of illumination on flowering is 

 essentially a matter of photosynthesis. Blue light, which decreases 

 photosynthesis, acts hke decreased illumination on flowering, while 

 in red Hght, by which photosynthesis is less affected, flowering 

 occurs. 



Various other conditions — ^temperature, water, nutritive salts, 

 etc. — have been found to influence the occurrence of flowering. In 

 summing up his experiments on flowering plants in general Klebs 

 says: 



For the formation of flowers the relations between the internal physico- 

 chemical conditions must be different from those in which vegetative growth 

 occurs. I believe that a quantitative increase in concentration of the organic 

 substances, with all its physical and chemical consequences, plays an essential 

 part in the transition from growth to reproduction. All external factors may 

 influence the occurrence of flowering favorably or unfavorably, according to 

 their intensity, their interrelations with each other, and the specific nature of 

 the plant, their effect depending upon the relations among the internal con- 

 ditions which they bring about.' 



In a later paper Klebs states the results of his extensive experi- 

 ments on Sempervivum funkii in somewhat more definite form. He 

 says: 



I begin with a vigorous, previously well-nourished rosette which is ready 

 to bloom and make the experiments which determine its fate before or during 

 •"he primordial stages of flower development. The results are as follows: 



' Klebs, '04, pp. 553-54. 



