( 363 ) 
Starting with a single cell which elongates (fig. 123), a 
spherical mass is soon formed which later becomes broadly 
pyriform (fg. 125) with no internal differentiation apparent. 
If a suspensor is formed at all it is of only transient character. 
In none of those embryos which had reached a multicellular 
state was there any evidence of a suspensor. 
Cucurbita 
The development of the ovules upon the placenta has 
already been referred to and the different phases of the pro- 
cess are indicated by text-figures 6, A to 6, D inclusive. As 
in the case of Cztrullus, the origin of the archesporium is 
obscure. The cells at the apex of the incipient nucellus are 
all of similar appearance, being of a highly meristematic 
character, until one larger than the others appears in an 
axial row separated from the epidermis by two or more cells, 
presumably the tapetum (fg. 727). This cell increases in 
size while the cells surrounding it segment irregularly. The 
sporogenous cell assumes a large size in this form and like 
the others becomes centrally situated in the nucellus ( fg. 728). 
The divisions of the spore-mother-cell appear to be regu- 
lar. The first division results in the formation of two equiva- 
lent cells (fig. 729), which again divide to form four potential 
megaspores. Of these the lowermost produces the embryo- 
sac ( fig. 129 a), the others soon showing signs of disorganiza- 
tion. At this stage of development the nucellus consists of a 
bulbous lower portion surmounted by a narrow prolongation 
of its tissue which extends upward through the micropyle. 
By this time the differentiation of the outer portion has 
reached that stage in which the integuments have enveloped 
the nucellus and contracted above to form the micropyle. 
The divisions of the spore nucleus which now follow pro- 
duce the embryo-sac in the usual manner. The course of 
development presents no features worthy of particular men- 
tion. After the eight-cell stage is reached the process of 
differentiation goes on as indicatedin Cztru//us. Figure 137 
represents a partially formed embryo-sac in which the syner- 
