396 PLANT PHYSIOLOGY 



the absorption of water is dependent upon the suction tension 

 of the transpiring leaves and, conversely, that the intensity of 

 transpiration depends on the conditions of the absorption of 

 water by the roots. The absorption of salts by the roots of plants 

 depends on the photosynthetic activity of the fohage and in 

 turn upon the elaboration of pigments in the leaves. The 

 utilization of photosynthate in growth is dependent upon the 

 absorption of nitrogen and mineral salts. 



Numerous examples of such reciprocal assistance by separate 

 parts of the plant could be cited, but the interrelations of organs 

 find their expression likewise in other directions, for instance, 

 in their mutual relations in development. 



The influence of the growing point upon the lower buds may 

 serve as a striking example of growth correlations. In many 

 plants, as for instance the sunflower, the stem does not branch, 

 though a bud is formed in the axil of each leaf. This bud remains 

 during the whole life of the plant in a dormant state; after matur- 

 ing of the seed, the whole plant dies, together with the buds that 

 have never manifested their capacity for further growth and 

 development. But as soon as the top of the growing stem is 

 cut, a few, or all the dormant buds begin to develop rapidly 

 into lateral shoots, each of which terminates in an inflorescence 

 that develops a number of seeds. This compensates somewhat 

 for the loss of the large inflorescence that should have terminated 

 the central axis. 



The influence of the top on the lower parts of the plant is very 

 clearly demonstrated in trees, especially in conifers, which are 

 distinguished by a very regular branching. For example, the 

 trunk of the fir tree terminates in a top bud surrounded at its 

 base by a crown of four to five lateral buds. In spring, shoots 

 develop from these buds, the main shoot growing exactly ver- 

 tically owing to its negative geotropism, while the lateral shoots 

 grow out at a definite angle to the main axis. 



If the top bud is injured, this directly influences the character 

 of the growth of the lateral shoots. Some or all of them begin 

 to grov/ vertically. The main axis is thus either replaced by a 

 shoot that formerly was a lateral bud, or several vertically 

 growing shoots may develop. If the entire top of the fir tree is 

 removed with all its buds, the functions of the main shoot are 

 transferred to one or several of the lateral branches, and their 



