[Chap. XXXI Initiation of flowers 337 



to the above question is impossible today, some of the facts relating to it 

 may be of more interest than the answer. 



The leaves of begonia may be used as a means of vegetative multipli- 

 cation; that is, if the base of a leaf which has been broken from a plant 

 is placed in moist soil, a complete individual plant will develop from 

 it. If the plant from which the leaf was taken is about to bloom, the new 

 individual that grows from the isolated leaf will grow but little and 

 bloom within a short time. On the other hand, if the original plant is 

 vigorously vegetative, the new individual from the isolated leaf will 

 grow much larger and for a long period of time before flowers develop 

 on it. From such experiments as these a German botanist (Julius von 

 Sachs ) suggested in 1893 that flower formation may be dependent upon 

 specific chemical substances made in the leaves. At that time, and for 

 several years later, the idea that a small amount of some chemical sub- 

 stance formed in the plant could have such a profound influence on its 

 development attracted little serious consideration. 



A few years later, another German botanist (Georg Klebs) began a 

 series of experiments in which he was able either to keep plants in a 

 vegetative state for many years or to bring about flower formation and 

 sexual reproduction in a relatively short time. He thought that all his 

 experimental data could be explained on the basis of the influence of 

 light, inorganic salts, and other external factors upon the nutrition of 

 the plants, especially upon the synthesis and accumulation of carbohy- 

 drates in relation to other products. He concluded that the initiation of 

 flower primordia is dependent upon a previous accumulation of physio- 

 logical conditions. 



In 1918, two American botanists (E. J. Kraus and H. R. Kraybill) de- 

 scribed their experiments with tomato plants in which the number of 

 flowers formed, flower development, and subsequent fruit development 

 varied with external conditions that influence photosvnthesis and protein 

 synthesis in plants. From the discussions in previous chapters (XIII- 

 XVI ) we are aware of the ways in which certain external factors could 

 be changed and thereby alter the relative rates of photosynthesis and 

 protein synthesis in plants. Following this report many investigators, 

 working with several kinds of plants, performed hundreds of experi- 

 ments in attempts to discover the relation of the relative amount of 

 carbohydrates and proteins to the development of all parts of plants. 



These investigators showed that no organ of a plant grows well unless 

 it is well supplied with both carbohydrates and proteins, or with the con- 



