LIFE STORY OF FERNS 209 
The fern prothallium and embryo compared to a seed. 
The fern prothallium, with the young embryo fern 
oN — < attached, might be com- 
RASHES ey : j ) pared to a seed of one of 
tie”) the higher plants, where 
the embryo is surrounded 
by a food tissue known as 
the endosperm, as in the 
maize. This endosperm is 
in fact a prothallium of 
the higher plant. In the 
FIG. 254. Pen halioan of fern, bearing the maize seed it is shown > in 
germ and sperm pockets. This is a view Fig. AA Some of It is still 












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from the underside, and shows the root- 
lets also. | left Inside 
the embryo case. But in the pea, bean, 

and acorn it is all used up as food by 
the embryo and stored in the cotyledons. 
The only way in which the prothallium 
with the embryo of the fern differs from 
the seed of the corn or bean is in the a 
fact that the prothallium is green (with e Zz 
chlorophyll), that it has been shed from “—* 
the spore case, and has been developed 
as an independent individual. If the 
3 Fie, 255. Embryo 
fern prothallium were not green, but “ gem stinattached to 
the prothallium. 
were wrapped around the embryo and ““?™™™™™ 
still in the spore case, it would be a seed. When the 
