430 BOTANICAL GAZETTE [NOVEMBER 
In the majority of chromatophores the starch grains lie radially 
about the pyrenoid, with their broad end toward the periphery 
of the plastid and the narrow end abutting on the pyrenoid (figs. 1, 
2,10). They are approximately equal in length, but vary in shape 
from cuneate to trapezoidal to rectangular (grains /, figs. 2, 3, 
10, 16). Their opposing faces are straight; the outer faces are 
rounded or straight. 
In many plastids there are minute grains in the periphery of 
the plastid (figs. 8, 10, 15, 16). Grains of all sizes from minute 
grains to the larger grains are also found. These intermediate 
grains are all cuneate in shape, if they lie between the larger grains, 
and always occur near the periphery of the plastid (figs. 8, 15, 16). 
Occasionally the starch grains are clustered irregularly about the 
pyrenoid (figs. 8, 15). In this case also the smaller grains are 
found in the periphery of the plastid. 
Discussion 
There are two opinions about the origin of starch grains in . 
algae. The majority of investigators believe that the pyrenoid 
is concerned in starch formation. MEvYER believes that the pyre- 
noid is not concerned in starch formation. The pyrenoid may be 
implicated in starch formation in either of two ways. Its sub- 
stance may be changed into starch, that is, it may form starch by 
fragmentation, as SCHIMPER (5, 6) and TIMBERLAKE (8) believed, 
or it may be an active starch-former by secretion. 
In Zygnema the substance of the pyrenoid is not changed into 
starch. This is shown by a comparison of the shape and position. 
of the starch grains and the shape and position of the pyrenoid 
and by an examination of the pyrenoid itself. If the starch is 
formed by fragmentation of the pyrenoid, there should be such a 
similarity in the contour of the two that the starch grain could be 
fitted into the edge of the pyrenoid as the parts of a puzzle fit 
together. If the grains are chipped out so that they come to lie 
radially about the pyrenoid, bands of the pyrenoid should lie 
between the starch grains. Even though the pyrenoid were to 
Erow and change shape after the formation of each starch grain, 
