SEED PLANTS 165 
goniate, and the egg thereupon begins to grow and 
develops into the embryo-sporophyte, while the sur- 
rounding cells of the gametophyte become filled with 
food-materials and 
are known as the 
“endosperm.” The 
wall of the sporan- 
gium now hardens, 
while the outer tissues 
of the integument 
become pulpy, so that 
the ripened seed looks 
very much like the 
fleshy fruit of a plum 
or cherry. 
That the Cycads 
represent a very an- 
cient type is shown 
by their fossil re- 
mains, which indicate 
that during the Mes- 
ozoic age they were 
among the most abun- 
dant plants. They 
occurred in greatnum- 
bers, and comprised 
many more genera 
and species, as well 
as individuals, than 
at present. 
Fic. 41 (Conifere).— A, a branch of a fe- 
male plant of the common yew (Taxus), 
one of the simplest Conifers ; ma, young 
female flower; fr, ripe fruit; B, a single 
female flower, consisting of an ovule, or 
macrosporangium, ma, surrounded by a 
number of scale-leaves; C, a section of 
the flower, showing the terminal spo- 
rangium (ovule), m, surrounded by the 
integument, in, and the scales, sc; D, 
section of an older ovule, showing the 
large macrospore (‘‘embryo-sac’’), sp; 
E, the ripe fruit, with one side of the 
cup-shaped aril, av, cut away to show 
the seed, s; the seed is the matured 
ovule, the aril a special structure which 
grows up about the seed; F, a male 
ower of Taxus, showing the umbrella- 
shaped sporophylls, each bearing sev- 
eral microsporangia upon the lower 
surface; G, a single sporophyll; mi, 
the sporangia; H, a leaf of Gingko, 
showing the fern-like form and vena- 
tion. (Figs. F, G, after Eichler.) 
The first evidences of the existence of 
Cycads occur in the Carboniferous rocks, but in small 
numbers ; but in the Mesozoic rocks, as already stated, 
