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DUNCAN S. JOHNSON 
large basal end of the embryo sac. Such a nucleus is perhaps espec- 
ially needed for the formation of the relatively broad cell walls that are 
at first formed in the endosperm. Possibly also the activity of the 
endosperm cells in nourishing the embryo, during seed -development 
and at germination, is more efficient because of the presence of these 
large nuclei in them. But these advantageous results of the process do 
not, of course, explain its causes which will pretty certainly be deter- 
mined only after experimental study. 
5. The development of the embryo and endosperm. — The fertilized egg, 
with its two nucleoli, or its single enlarged nucleolus, remains undivided 
and unchanged, except for an increase in size, during the aggregation 
and fusion of the endosperm-forming nuclei and even during the first 
division of the fusion nucleus. Soon after this the oospore, or embryo, 
divides by a longitudinal wall and then by walls in other planes, 
whose sequence is undetermined, to finally form in the ripe seed, a 
suspensorless, slightly elongated embryo of about 50 cells. 
The large, lobed, central endosperm nucleus has 20 or more nuc- 
leoli. It divides mitotically by a huge spindle whose axis is transverse 
to that of the sac and which has on it 144 or more chromosomes. The 
second and third series of walls in the endosperm are approximately 
longitudinal and these are followed by irregularly placed walls that 
form an ellipsoid mass of 100 or more cells in the ripe seed. The en- 
dosperm is cellular from the start, each mitosis from the first is accom- 
panied by the formation of a cell plate and wall. The cells of the 
mature endosperm have large, lobed nuclei and rather dense cyto- 
plasm, containing many oil globules but no starch. 
This mode of development of the endosperm, in which a cell wall 
immediately follows each division of the nucleus, cannot be regarded 
as the most primitive type occurring among seed plants. I have al- 
ready pointed out (Johnson, 1905, p. 31), that this mode of endosperm- 
formation is one not found at all among gymnosperms and occurs 
elsewhere among angiosperms only in forms that are generally recog- 
nized as rather highly specialized forms. This same point has been 
more fully elaborated by Samuelsson (1913, pp. 135-145). Moreover 
this succedaneous type of formation of endosperm cells is not encount- 
ered among pteridophytes, save in two highly specialized families, the 
Marsiliaceae and Salviniaceae, neither of which can be thought of as a 
very probable ancestor of angiosperms. 
6. Germination and the storage of food in the perisperm. — At germi- 
