628 Kershaw. — Structure and Development of the 
Shortly after the beginning of active independent growth of nucellus 
and integument, the megaspore mother-cell begins to increase in size, and 
the reduction divisions occur. These have not been observed, but the 
result, a row of three cells, is shown in Fig. 3, PL LXI, which is taken from 
an ovule slightly younger than the one represented in Text-fig. 2. The 
upper two cells are smaller and their nuclei less dense than the lowest one, 
which becomes the embryo-sac. The same development of the embryo-sac 
is described in Ceratozamia 1 and in Stangeria . 2 From this time a marked 
increase in size of the embryo-sac is noticed, and the sister cells show signs 
of disorganization (Fig. 4, PL LXI). The nucleus of the embryo-sac divides 
Text-fig. 5. Portion of longitudinal section of ovule represented in Text-fig. 3, showing sporo- 
genous tissue surrounding the embryo-sac. e. — embryo-sac ; d.s. = degenerating sporogenous cells ; 
s. = active sporogenous tissue ; f = flattened cells of nucellus, bordering on the integument, x 300. 
into two, which are shown in Fig. 5, PI. LXI, with the disorganized sister 
cells above. Other sections obtained show the result of a second division, 
an embryo-sac with four free nuclei. 
Free nuclear division proceeds and the embryo-sac gradually enlarges, 
but the protoplasmic contents do not increase at an equal rate, and hence it 
appears for a long time as a hollow sac with a thin lining of protoplasm in 
which lie the free dividing nuclei (Fig. 6, PL LXI). 
The growth of the embryo-sac is accompanied by growth of the 
surrounding sporogenous tissue. Many of these cells are actively dividing 
1 Treub, loc. cit., 1885. 
2 Lang, loc. cit. 
