DIGESTION 249 
general appearance ; the other, diastase of secretion, dis- 
integrates it by a process of corrosion before dissolving it 
(fig. 123). The first of the varieties has a very wide 
distribution in plants, being present 
almost everywhere. The second is Q@ (y 
the body formed by the glandular 
covering or epithelium of the scutel- A 
lum of the grasses. 
The great function of diastase in fic. 193—Srancn Grarns 
the plant is to transform starch (and  AyPPgSS OF DIGES- 
probably glycogen where it occurs) eee 
into maltose or malt-sugar. Wher- 
ever starch is formed, whether in the living leaf or in the 
reservoir set apart for storage, it must be regarded as a 
reserve material, and its removal from the seats of deposi- 
tion is preceded by its conversion into this sugar. The 
details of the transformation are not fully known at present, 
but a good deal of information has been obtained through 
the labours of many observers. Starch has a rather large 
molecule, but its exact formula is not thoroughly known. For 
a long time it was taken to be approximately n(C,H,,0,), 
and the value of m was thought to be 5. More recently the 
suggestion has been made that the molecule is much larger, 
and may be more truly represented by 5[(C,,H,,0,,)o9], the 
view being based upon the formation of several complex 
substances during its decomposition. The starch molecule 
is possibly composed of four dextrin-like groups, each 
(C,,H,,0,,)o) arranged about a fifth. It has been suggested 
that the first action of the diastase is the liberation of these 
from one another; and that four of them by successive 
incorporations of water are converted, through a series of 
complex substances called malto-dextrins, into maltose, 
while the fifth withstands the action of the enzyme for a 
considerable time. After the action of the diastase has 
been proceeding for some time the resulting product is 
found to be four parts maltose and one part dextrin. 
‘How far this series of decompositions represents what 
