262 VEGETABLE PHYSIOLOGY 
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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 
markec 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 
