191 2] Morphology and Biology of Insect Galls 371 



proliferation of gall tissue. The larva consequently by accelerating the 

 rate of change from starch to sugar is indirectly stimulating the proto- 

 plasm and thus controlling the growth of the gall. The general principle 

 is applicable here that the available food supply governs very largely the 

 size of an organ and consequently must influence the activity of its pro- 

 toplasm. It is interesting to note in this connection that the size of the 

 gall and the contained larva are directly proportional to each other. 

 The relations between the two are reciprocal. The larger larva ensures 

 a greater enzyme production and hence a more abundant food supply 

 and presumably a larger excess for the stimulation to cell proliferation. 

 The amount of enzyme action appears clearly to be proportional to the 

 size of the larva. The evidence seems conclusive that the nutritive zone 

 functions as an organ for preparing soluble food materials for both the 

 larva and the gall. This evidence receives further confirmation from the 

 fact that in addition to the empty cells lining the larval chamber there 

 are others scattered throughout the nutritive zone often to its outermost 

 layers (Fig. 59). This also seems to point to the conclusion that the con- 

 tents of these cells have been used in supplying food for the proliferation 

 of tissue in the other parts of the gall. 



Summing briefly, the larva secretes an enzyme, capable of changing 

 starch to sugar, which acts on the starchy constituents of the nutritive 

 zone and accelerates the rate of their change to sugar. The material 

 thus prepared supplies nourishment for both the larva and the gall. The 

 protoplasm of the latter is thus rendered unusually active since it re- 

 ceives an abnormal quantity of available food material in a limited area. 

 The hypertrophy and cell proliferation and probably also the appear- 

 ance of vestigial tissue or other primary characters are the response of the 

 protoplasm of the host to the additional food supply. 



Attempts were made to substantiate this theory by further and more 

 direct experiment. Diastase in solution was injected into seedling 

 Windsor beans at different points with the purpose of stimulating the 

 tissues to increased cell proliferation. When the place selected was just 

 below the arch of the hypocotyl, a decidedly large callus was obtained in 

 some of the experiments. These were not conclusive, however, owing to 

 the variation in size of the normal plant in that region and the very great 

 if not insurmountable difficulty of detecting increased callus formation 

 when only differences in amount are to be expected. It is further very 

 difficult to simulate the action of the producer-larva in bringing the 

 diastase into contact with the proper tissue. 



The discovery of an enzyme as an exudation from gall-producer larvae 

 recalls the statement of Laboulb^ne'® that he had induced cell proliferation 

 by injecting into plant tissue the water in which larvae had been washed. 



