140 
MORPHOLOGY 
FIGS. 
cells contribute to the nutrition of 40-75 mother cells that function. 
These mother cells become relatively very large and produce large 
spores, the total output of megaspores being 
150-300 (fig. 317). Both kinds of spores 
escape by the decay of the sporangium 
wall. 
Male gametophyte. The male gametophyte 
is still more simple than that of Selaginella (figs. 
318-320). It consists of a single vegetative 
cell and a single antheridium, as in Selaginella; 
but the sperm mother cells are only four in 
number. This is the lowest number reached 
among pteridophytes, and the nearest approach 
318-320. Male to seed pi antS) among 
gametophyte of Isoetes .'318, , . , , 
stage showing the vegetative which the sperm mother 
cell (at bottom and without cells are reduced to two. 
nucleus) and the antheridium The S p er ms are large, 
(with three wall cells visible . ... 
and the central primary sper- Spirally COlled, and 
matogenous cell); 319, older multkiliate (fig. 320), 
stage, in which the wall cells such as characterize all 
have broken down and the . -11 
four mother cells (each con- other pteridophytes 6X- 
taining a sperm) are free CCpt Lycopodiales. It 
in the antheridial cavity; ' K th i s feature of Isoetes 
320, sperm. After BELA- 
JEFF> that perhaps presents 
the greatest obstacle to 
including it among Lycopodiales. 
Female gametophyte. The female gameto- male gametophyte 
phyte develops in the same general way as does Isocies: N 321 (aft , er HOF ' 
r J r . MEISTER), complete ga- 
that of Selaginella, but with some interesting me tophyte, bearing an 
differences. After the free nuclear divisions, archegonium whose neck 
followed by the formation of an apical tissue, a | exposed through a crack 
J in the megaspore wall 
layer of cells develops completely about the ( not shown); 322 (after 
cavity of the megaspore and then grows centripe- CAMPBELL), archegonium, 
tally until the megaspore is filled with tissue sh wing , two tien5 , of neck , 
J cells and an axial row of 
(fig. 321). The growth of this tissue is precisely t h re e cells (nock canal 
like the growth of the endosperm tissue (female cell, ventral canal cell, 
gametophyte) in gymnosperms (p. 196 ). The 
gametophyte of Isoetes does not protrude through the broken megaspore 
wall and develop tissue outside, as in Selaginella, but is exposed only 
322 
FIGS. 321, 322. Fe- 
of 
