254 VEGETABLE PHYSIOLOGY 
decompose respectively carbohydrates, proteins, glucosides, 
and fats or oils. In nearly every case the action of these 
enzymes is one of hydration, the body acted upon being 
made to take up water, and to undergo a subsequent 
decomposition. 
Of those which act upon carbohydrates we have two 
varieties of diastase, which convert starch into maltose, or 
malt-sugar ; imulase, which forms another sugar, levulose 
or fructose, from inulin; invertase, which converts cane- 
sugar into glucose and fructose; glucase or maltase, which 
produces grape-sugar from maltose; and cytase, which 
hydrolyses cellulose. Another enzyme, which does not 
appear to be concerned with digestion so directly as the 
others, is known as pectase; it forms vegetable jelly from 
pectic substances occurring in the cell-wall. 
The members of the second group act upon protein 
substances, and are technically known as proteoclastic 
enzymes. The principal members of this group are peptase, 
the various iryptases, and ereptase. Peptase and tryptase 
convert albumins and globulins into peptones, the tryptases 
also decomposing certain peptones into amino- and amido- 
acids ; while ereptase has only the power of effecting the 
last-named change. . Allied to these is rennet, which converts 
the caseinogen of milk into casein, the characteristic protem 
of cheese. It occurs in a great many plants, but its function 
in vegetable metabolism is unknown. 
The enzymes which act upon glucosides are many; the 
best known are emulsin and myrosin ; other of less frequent 
occurrence are erythrozym, rhamnase, and gaultherase. 
Those which decompose fats have not been so fully inves- 
tigated: they are known as lipases, but whether there are 
many different varieties or not has not at present been 
ascertained. 
Diastase appears to exist in two varieties, distinguished 
from each other by their mode of action on the starch 
grain, One, called diastase of translocation, dissolves the 
grain slowly from without inwards, without altering its 
