16 
PLANT MORPHOLOGY. 
Structure and Composition. — The formula which is 
generally accepted for starch is (C ri H 10 O 5 ) n , this being 
recognized by Pfeffer, Tollens and Mylius. It is sup- 
posed that the molecular composition is quite complex, 
the grain being composed of different single groups of 
C 6 H 10 O 5 or multiples of the same. While this formula 
may be accepted in a general way, still it has been 
shown that there are at least two substances which 
enter into the composition of the starch grain, and 
more recent studies tend to show that it is in the nature 
of a spliero-crystalloid, resembling inulin in some 
respects. The starch grain has an interesting struc- 
ture. In form it is more or less spherical or polygonal ; 
has a more or less distinct marking known as the 
“ hilum,” “ nucleus ” or “ the point of origin of growth,” 
and the substance is distributed in more or less dis- 
tinct layers or lamellse. 
While starch grains usually occur singly, they 
are not infrequently found in groups of two, three or 
four grains, when they are spoken of as two-, three-, or 
four-compound. In some of the cereals, as rice and 
oats, they are 100-compound or more. The individuals 
in compound grains are in some cases easily separated 
from one another. This occurs frequently in the mount- 
ing of specimens, and is especially noticeable in the 
commercial starches. 
The various commercial starches are in the nature 
of reserve starches and may be distinguished by the 
following characteristics : 
(1) The shape of the grain, which may be spherical, 
ellipsoidal, ovoid, polygonal, or of some other charac- 
teristic form. 
(2) The size of the grain, which varies from 1 or 2 
ft to about 100 n in diameter. 
(3) The position of the point of origin of growth, 
