8 



PHYTOHORMONES 



external forces such as light and gravity, — correlations, 

 normal development, galls and monstrosities were brought 

 into one picture. 



In his very remarkable publications on galls Beijerinck 

 (1888, 1897) elaborates the idea of ''growth-enzymes." 



Fig. 2. a, b, c, gall of Nematus capreae on leaf of Salix. a, egg deposited with 

 some mucilage in mesophyll of young leaf; b, mature gall before hatching of 

 larva; c, gall in which Ijy accident no egg has been deposited. The mucilage 

 excreted by the gall-wasp has caused formation of an almost complete gall. 

 This excretion is the first published example of an organ-forming substance. 

 (From Beijerinck, 1888.) d, gall of Cecidomyia Poae on stem of Poa, showing 

 excessive root formation. (From Beijerinck, 1885.) 



While he originally thought (1886) that ''it can not be 

 doubted that nutritive stimuli must be considered as the 

 primary cause" of root formation when parts of plants are 

 cut off from the parent-plant, he afterwards modified his 

 views in the direction of those of Sachs. In the case of the 

 Capreae-gsdl on Salix (Beijerinck, 1888) he considers the 

 development of the gall (see Figure 2) to be caused by "a 

 protein, whose action differs from that of ordinary proteins, 

 which only form an equivalent amount of protoplasm, and 

 resembles that of an enzyme, whose effect is quantitatively 

 of a different order of magnitude from the amount of active 

 material." Thus we have to do here with a "material 



