REPRODUCTION 345 



Other types of plants are characterized by repeated blooming. 

 Here belong the great majority of perennials and woody plants. 

 They blossom and fruit every year. Still that does not prevent 

 their further vegetative growth. The duration of their life is prac- 

 tically unlimited. What inner physiological readjustments enable 

 them to continue their vegetative growth after fruiting is at pres- 

 ent unknown. 



In general, there is a certain antagonism between vegetative 

 growth and reproduction, which is especially marked in plants 

 that bear fruits but once, and less manifest in plants that bear 

 fruit repeatedly. 1 This antagonism is frequently attributed to the 

 struggle for the nutritive substances which have accumulated in 

 the plant. Analyses have shown that in the sunflower or the corn 

 plant, for instance, almost all of the nutritive substances pre- 

 viously stored in the stems, the leaves, and even the roots are 

 transferred to the ripening fruit. This phenomenon can be 

 observed to a still greater degree in root crops. This evacuation 

 of substances, however, cannot be the only cause of dying, for if 

 the working capacity of the leaves and the roots were preserved, 

 these losses might be compensated easily. The cause of this 

 behavior should be sought in the quantitative changes of some 

 hormones, which regulate growth and other life activities of the 

 plant. Dying of plants may be regarded as a phenomenon analo- 

 gous to senescence of an animal organism. 



100. Effects of Environment on Time of Fruiting. Photo- 

 periodism. — The exact causes which initiate reproduction are 

 unknown. Several methods, however, are known by means of 

 which reproduction either may be accelerated or delayed, or made 

 more abundant. A detailed study of these methods is not only of 

 great practical value for accelerating the time of a harvest, but 

 also of great theoretical interest, as by this means it may be possible 

 to approach the solution of the question as to the causes which 

 determine the time of fruiting. 



It has been noted for some time that the conditions of nutrition 

 of a plant have a striking effect on both vegetative and reproduc- 

 tive development. Light seems to be of the greatest importance in 

 this respect. If a plant is grown under conditions favorable in all 



1 Many plants with a continuous type of growth, like the tomato, some 

 crucifers and legumes, though flowering repeatedly, show a distinct antagon- 

 ism between vegetative growth and sexual reproduction. 



