262 
MORPHOLOGY 
becomes curved, the micropyle being directed thus towards the surface 
of origin; such ovules are called campylotropous (fig. 583), and they are 
much less common than the other kinds. Far the most common kind of 
ovule among angiosperms is one which develops a stalk (funiculus) that 
becomes curved at the apex, so that the body of the ovule lies against it, 
and although the axis of the body is straight, the micropyle is directed 
towards the surface of origin; such ovules are called anatropous (in- 
verted), the funiculus appearing as a ridge along one side of the body of 
the ovule (figs. 581, 584). The advantage 
of the anatropous ovule may be recognized 
when it is remembered that the pollen tube 
is advancing along the wall of the ovary, 
and the micropyles are thus brought near the 
wall. 
Development. The megasporangium 
(really the nucellus) is eusporangiate in its 
development, resembling the microsporan- 
gium at every stage. There is usually a 
single hypodermal initial cell, which is soon 
recognized among the other hypodermal 
cells by its larger size and the different ap- 
pearance of its contents (fig. 585). Some- 
times there are two or more of these initial 
FIGS. 585, 586. Develop- cells, as is the usual case in microsporangia. 
ment of megasporangium of The large hypodermal initial divides by a 
periclinal wall into two cells, the outer cell 
being the primary wall cell, the inner one 
shaded one) and primary spo- being the primary sporogenous cell (fig. 586). 
rogenous cell. After CHAM- mu 11 11 L j- -j /c o \ 
E RLAIN The wall cell may not divide (fig. 587), or 
there may be one or more divisions (fig. 588), 
or in some cases there may be several wall layers developed, as in 
microsporangia. The primary sporogenous cell does not divide and 
form more sporogenous cells, and therefore it is the megaspore mother 
cell. This means that when it divides, a tetrad is formed by two 
successive divisions, which are the reduction divisions. The tetrad of 
megaspores is almost always a linear row (fig. 587), which is an ex- 
ceptional arrangement among microspores. It is very seldom that 
more than one of the megaspores matures, and that one is almost 
invariably the innermost one of the row, that is, the one farthest from 
586 
Salix: 585, single hypodermal 
initial; 586, division of initial 
into primary wall cell (outer 
