268 VEGETABLE PHYSIOLOGY 
of these. A cell which is about to secrete is generally 
found to be filled with colourless hyaline protoplasm in 
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 
seutellum of the barley grain, which we have seen produces 
considerable quantities of diastase. The first stage of the 
process ig 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 com- 
pletely 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 vacuo- 
lated as at first. 
Following the anabolic changes we have thus the breaking 
down of the protoplasm, attended by the appearance 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 
