400 PHYSIOLOGY 

especially in leaves and storage organs. It partly digests starch into 
maltose, a residue, representing about 20 per cent of the grain, resisting 
its action for a long time. In the course of decomposition, various 
dextrins are produced by successive cleavage, presently becoming simple 
enough to be analyzed. The last member of the series breaks into mal- 
tose and isomaltose, C 12 H 2 2O 11 . There are at least two forms (possibly 
more), secretion diastase and translocation diastase, differing in the 
mode of dissolution of the starch grain. The former erodes the surface 
irregularly, whence narrow canals penetrate the interior, and the grain 
often falls into fragments; the latter corrodes the grain almost evenly, 
reducing it gradually in size until it disappears. 
It is probable that what is here called diastase consists of at least two enzymes ; 
amylase, which digests starch to a dextrin, and dextrinase, which breaks the dextrin 
into maltose; this, maltase (see below) cleaves into glucose. 
Invertase, in like manner, can hasten the hydrolysis of cane sugar 
into two hexose sugars, glucose and fructose. 
Trehalase and several other enzymes in fungi attack trehalose and other 
sugars peculiar to them, and digest them into the hexoses of which they 
were originally built. 
Maltase) an enzyme which is often associated with diastase, carries 
the process of starch digestion further, cleaving each maltose molecule 
into two molecules of glucose. 
Inulase likewise attacks inulin, breaking it up into levulins and finally 
into fructose. Perhaps there is here also more than one enzyme at work. 
Cytase is responsible for digesting hemi-celluloses (chiefly mannans 
and galactans) of seeds, while enzymes under the same name, but prob- 
ably different, have been found in wood-destroying fungi, and have been 
assumed present whenever a tissue is penetrated by a hypha, or by a 
more massive member, as in the sinking of the foot of bryophytes into the 
gametophyte (see Part I, p. 108) and in the emergence of the branches of 
roots through the cortex (fig. 667; see also Part I, p. 250, and fig. 558). 
Fat enzymes. Lipase, perhaps of several different forms and so 
deserving distinctive names, has been found in organs where fats are 
present, especially in seeds and many fungi. Lipase breaks up fats into 
their components, fatty acids and glycerin, which are then readily dif- 
fusible. 
Glucoside enzymes. These are common, setting free glucose from many dif- 
ferent compounds. Emulsin, for example, breaks amygdalin, a glucoside common 
