262 VEGETABLE PHYSIOLOGY 



which certain vacuoles may be seen. Immediately before 

 secretion begins an increase of the amount of the protoplasm 

 can be observed, which is effected at the expense of various 

 nutritive products which are transported to it. During the 

 whole of the process, when this is prolonged, such a supply 

 of nutritive material takes place. If during the secretion this 

 supply is stopped, the process is rapidly suspended. This 

 can be detected easily in the case of the epithelium of the 

 scutellum of the barley grain, which we have seen produces 

 considerable quantities of diastase. The first stage of the 

 process is thus evidently anabolic. As soon as the nutrition 

 of the cell has reached a certain point the appearance of 

 the protoplasm undergoes a change. Minute granules 

 begin to be formed in its substance, which increase in 

 number until the hyaline character is replaced by a 

 marked uniform granularity, the cell substance becoming 

 somewhat like ground-glass in appearance. The growth 

 of the protoplasm and this subsequent formation of 

 granules lead to the obliteration of the vacuoles, till the 

 cell is completely filled. After a time as the secretion 

 leaves the cell the latter shrinks again ; the granules are 

 passed out in solution in the sap which is exuded, and the 

 protoplasm is seen to be less plentiful and to become 

 hyaline and vacuolated as at first. 



Following the anabolic changes we have thus the 

 breaking down of the protoplasm, attended by the appear- 

 ance of the granules to which it has given rise. There is 

 reason to believe that the granules consist of the zymogen 

 rather than the enzyme and that the final transformation 

 of the former into the latter takes place just as the exuda- 

 tion of the sap occurs. 



In glands in which the process of secretion is repeated 

 more than once, similar changes may be traced. The 

 secretion of the enzyme in these cases can be shown to 

 take place by successive stages. The preliminary hyaline 

 condition is followed by the granular one, and in this state 

 the cell can remain for some time before the enzyme is 



