8 Campbell . — 77 ^ Development of the Flower and 
The very young stamen, cut parallel to its broad face 
(Fig. 5), is broadly conical, slightly constricted at the base, 
thus indicating the differentiation of anther and filament. 
In this stage it is composed of nearly isodiametric paren- 
chyma. but shows the definite divisions of the tissues into 
dermatogen, periblem, and plerome, referred to in connexion 
with the original primordium. The plerome in this view has 
a broadly conical form, with two lateral outgrowths marking 
the position of the future loculi. A cross-section of a similar 
stage shows that there are really four of these. 
A cross-section of a somewhat older stage is shown in 
Fig. 7. While there is in general the same arrangement 
of the tissues seen in the younger stamen, the loculi are more 
clearly defined. The two upon the outer side are somewhat 
broader than the others, and between them there is a small 
sterile lobe. Each loculus shows much the same arrangement 
of the tissues as the whole of the young staminal rudiment, 
and the origin of the sporogenous tissue is plainly traceable 
in all cases to the plerome. The latter is usually well defined, 
and forms a conical mass, usually three or four cells wide 
at the base, and narrowing above. The periblem, which 
at first is but one cell thick, later, by the formation of 
periclinal walls, becomes thicker, and finally the limits 
between it and the plerome are no longer distinguishable. 
In cross-section at this stage, there may be seen two vascular 
bundles near the base of the inner loculi. The exact origin 
of the sporogenous cells is difficult to trace, but there seems 
no question that they originate from the outer cells of the 
plerome, and that the archesporium is not of hypodermal 
origin as is usually the case. In this respect Lilaea agrees 
with Naias jlexilis , and probably also with Zannichellia , 
although in the latter the question is not quite clear 1 . 
At first the young sporogenous cells are not readily distin- 
guishable from those surrounding them, and it is quite 
impossible to trace them back certainly to the division of 
1 Campbell, 1. c., pp. 13 and 41. 
