1913] GOW—MORPHOLOGY OF AROIDS 139 
into the ovule is probably determined by the presence of nutritive 
material in that quarter, since the nucellar cells, and even the tip 
cells of the integuments often become somewhat swollen and 
glandular and break down readily. If this be the case, the tube 
should enter a sterile ovule quite as readily as a fertile one. Ina 
number of cases remains of shrunken pollen tubes were observed 
near or in contact with sterile nucelli (fig. 40). 
The sterile nucellus finally breaks down, the process usually 
beginning within, and sometimes resulting in, the formation of an 
interior cavity before the disin- 
tegration of the outer cells (figs. 40, 
41), and the nuclei of the cells oc- 
casionally lie free in this cavity 
before disintegration. The break- 
ing down of the nucellus finally 
leaves the cavity within the in- 
teguments completely empty; the 
ovule soon collapses and begins to 
decay. ; 
In the case of fertile ovules, 
the embryo sac is of the usual 
8-celled type. The cavity soon 
becomes filled with a mass of thick- 
walled endosperm cells, and the Fic. 41.—Richardia africana: sterile 
endosperm is persistent in the nucellus; disintegration just beginning. 
seed. The proembryo develops a 
little later than the endosperm, and is spherical in shape, finally 
lengthening out and developing a distinct notch (fig. 42). 
Anthers dissected out, before the appearance of the flower bud 
as a swelling under the leaf-sheath, disclosed many large multi- 
nucleate mother cells. Tetrads are formed by successive divisions, 
the 4 daughter cells lying in the same plane. Material taken from 
a plant in which the flower bud was beginning to form a prominent 
swelling within the stem disclosed mature pollen grains filling the 
loculus of the anther. The latter has the usual thickened epidermal 
layer of rather small cells, inside which is an endothecium of large 
cylindrical cells with riblike thickenings. The tapetum consists 


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