1904] WYLIE: ELODEA CANADENSIS 7 
those in the antipodal pouch. The general evidence, however, 
is against this view. The irregular number of nuclei displayed 
here and the general arrangement of the cytoplasm about them 
would indicate that any increase in number has come from 
divisions among the antipodals—an activity in this region that 
often results from fertilization. In all embryo sacs studied at 
earlier stages the lower polar had passed out of the tip, and its 
return to the antipodal group seems here improbable. 
THE MICROSPORANGIUM. 
The stamens are very short-stalked, the sporangia being 
practically sessile, and are further’ characterized by a relatively 
small amount of sterile tissue. Each stamen develops only two 
sporangia, there being no suggestion of a greater number at any 
stage. This condition seems to occur regularly in but a limited 
number of forms. The presence of only two sporangia to the 
stamen has long been known for the Asclepiadaceae, and has 
recently been reported by Shoemaker (15) for Hamamelis. 
The occurrence of this phenomenon in such widely separated 
and differently specialized forms offers no clue to its signifi- 
cance. 
The developing stamen is at first circular, later becoming 
oblong in cross-section. From a homogeneous meristematic 
mass there differentiates at either side of the stamen a hypo- 
dermal archesporial column (fig. 43). These cylinders of tissue 
extend the whole length of the stamen and have from five to 
eight cells each in cross-section. They are separated by a mass 
of sterile cells which later develops the rudimentary bundle and 
contributes somewhat to the tapetum of both sporangia. The 
archesporial cells become quite distinct, differing from these 
sterile cells in size and staining reactions. 
In the establishment of the primary wall layer the divisions of 
the archesporial cells are not simultaneous, the outer ones tending 
to divide a little earlier than those nearer the body of the 
stamen. It follows, from the form of the siamen and the extent 
and location of the archesporium, that the primary wall layer 
nearly invests the column of primary sporogenous cells, and this 
investment is made more nearly complete in places by the 
