414 PLANT PHYSIOLOGY 



This effect of light, however, is more of an indirect than of a 

 direct nature. Plants that have a considerable storage reserve 

 of organic substances, especially carbohydrates, will bloom even 

 in darkness. The hyacinth and other bulbous plants are good 

 examples of such behavior. Similarly, it is possible to obtain 

 flowers on separate branches of a plant, which are placed for 

 this purpose in a dark chamber, provided that their organic 

 connection with other parts of the plant remains intact and the 

 rest of the plant is exposed to strong light. On the basis of 

 these facts, Klebs was led to the idea that light hastens the 

 period of blooming chiefly by assisting the plant to accumulate 

 carbohydrates and that the latter is the direct cause of the change 

 from the stage of vegetative growth to that of reproduction. 



This has been confirmed by experiments with plants grown 

 under different kinds of colored glass, each representing a certain 

 part of the spectrum. In red light, plants bloom almost as 

 readily as in white light ; while blue hght delays blooming, despite 

 the fact that the formative effect of light depends chiefly on 

 exposure to blue rays. Analyses have shown that plants grown 

 in red Hght are much richer in carbohydrates, both starch and 

 sugars, than those grown in blue light. 



Besides the carbohydrates, the amount of mineral substances 

 and various nitrogen compounds also is of importance in deter- 

 mining the time of fruiting. It has been noted for a long time 

 that nitrogenous fertilizers increase the vegetative growth of a 

 plant at the expense of its reproductive functions. According to 

 Klebs, it is not the absolute amount of particular substances 

 that determines the time of fruiting, but their proportional 

 relation. A preponderance of carbohydrates over nitrogen and 

 mineral compounds leads to blooming and fruiting; a reverse 

 relationship, to vegetative development. Hence, by combining 

 certain fertilizers and by other cultural methods, one may pro- 

 duce in the plant either an accumulation of carbohydrates or an 

 increase in nitrogenous compounds, thus making it possible to 

 control to a certain extent the development and behavior of 

 plants (Kraus and Kraybill). 



A number of methods used by fruitgrowers, for the purpose 

 either of accelerating blooming or making fruit production more 

 abundant, are based also on the relationship between carbohy- 

 drates and soil nutrients. Transplanting, the cutting of roots, 



