ie Of DOGONITIACE AE 17 
that by the stretching thickening ring which is becoming bulged 
out, forming the oogonium. A second thickening ring then 
develops in the median region of the young oogonium followed 
by a transverse rupture of the wall at this point; the septum 
formed in connection with this second division lies on a level 
with the top of the first-formed sheath, so that the supporting- 
cells are included in the latter. This curious development .is 
responsible for the fact that the wall of the mature Bulbochaete 
oogonium can nearly always be seen to consist of three pieces.”’ 
(West and Fritch 1927, p. 219). (Cf. Pl. LXIV, figs. 641-645.) 
If the lower of the two suffultory cells is the longer we speak 
of the division as supreme, superior, or supramedian, depending 
upon the relative lengths; if the upper is the longer of the two, 
the division becomes inframedian, inferior, or basal; if the two 
are equal in length, the division is median. In some species of 
Bulbochaete the position of the division is variable and cannot 
always be depended on as a distinctive diagnostic characteristic. 
If the two divisions are at right angles to the long axis of the 
vegetative cell, the oogonium is said to be erect; if one division 
is oblique, giving one suffultory cell a five-sided, or five-angled, 
appearance (viewed in optical section), the oogonium is patent. 
In members of the genus with globose (or nearly so) oogonia, 
the upper and not the lower suffultory cell is five-angled, while 
in those with more ellipsoid oogonia the reverse is true. In the 
latter case the upper cell is quite small, or may not be visible. 
A patent oogonium is always formed by a division of the basal 
cell of a side branch, with which may be associated a bulbous 
hair, an androsporangium, an antheridium, or rarely a vegetative 
cell. An erect oogonium on the other hand forms from a division 
of some vegetative cell other than the basal one. In the 
globose forms of the genus, patent oogonia are common while 
erect oogonia occur only in a few species. Among the ellipsoid 
forms both kinds are found. (Pl. LXIV, figs. 641-645). 
The oogonium contains a single egg and varies considerably 
in shape, being largely ellipsoid, ovoid, globose, or some variation 
of these shapes. It is usually of noticeably larger diameter 
than the vegetative cell, although in Oe. capillare and in a few 
others the difference is not great. The oogonium wall is rarely 
internally ribbed (as in Oe. acrosporum), punctate (as in Oe. 
minus), plicate (as in Oe. megaporum, Oe. platygynum) or 
provided with a transversely disposed ring of conical warts 
(as in Oe. itzigsohnit); in most species it is smooth. The 
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