1913] YORK—DEN DROPHTHORA 203 
these cells had become turgid and crowded closely together into a 
very compact layer (fig. 55). 
In the ripe seed the outer layer of cells contains large quantities 
of a fatty substance which stains black in osmic acid and dark 
blue in cyanin (figs. 53, 54). When germination begins, the fat, 
as indicated in figs. 53 and 54, almost entirely disappears from them 
and they become practically colorless. Large brown cystoliths, 
the chemical nature of which was not determined, were found in 
some of the cells. The remaining cells contain starch and other 
food substances which are more or less limited to certain portions. 
Fatty substances as seen in the outer cells also occur in the inher 
region of the endosperm and are in greatest abundance in the 
chalazal part (fig. 53). There is a single layer of cells, densely 
filled with chloroplasts and starch, subjacent to the outer cells 
(fig. 55, cl). The cells adjacent to the cotyledons (fig. 55, 7) 
contain practically no chlorophyll and very little starch, but sub- 
stances which stain like proteins. Immediately above this layer 
the cells are abundantly filled with starch (fig. 55, 3). The remain- 
ing portion contains less starch and chlorophyll, but in addition 
has large cystoliths of calcium oxalate (fig. 55, cs). The cells of the 
embryo are also well supplied with chlorophyll. When germina- 
tion begins, the chlorophyll present in the seed becomes greatly 
intensified. It is important to note in this connection that chloro- 
phyll is most abundant in the cells just below the outer layer of 
cells which become almost colorless when germination occurs. 
The chlorophyll in the endosperm is manifestly for photosynthetic 
work, as a result of which food is furnished to the young plant 
until it becomes fixed on its host. It becomes more evident that 
the chlorophyll performs the work of photosynthesis from the fact 
that the seeds will not germinate in the dark nor will germinating 
seeds continue to develop if kept from the light. A number of 
attempts to germinate seeds of D. opuntioides in a dark chamber 
in the laboratory were made, but all failed. Also small dark 
chambers were constructed out of black paraffined paper over seeds 
that had been dropped on the branches by birds. At the end of 
four weeks these seeds had not germinated, while uncovered seeds 
near those which were covered had germinated. Seeds of Den- 
