302 ESSENTIALS OF BOTANY 
evident without careful examination. The pistil is the 
megaspore-producing leaf, or megasporophyll, and the sta- 
men is the microspore-producing leaf, or microsporophyll. 
Pines and other gymnosperms produce a large cell (the em- 
Fic. 218. Longitudinal Section 
through Fertilized Ovule of a 
Spruce. 
p, pollen grains; ¢, pollen tubes; 
n, neck of the archegonium; 
u, body of archegonium with 
nucleus; e, embryo sac filled 
with endosperm. 
bryo sac) in the ovule (Fig. 218) 
which is the megaspore, and a 
pollen grain which is the micro- 
spore. In its development the 
megaspore produces an endo- 
sperm or small cellular prothal- 
lium, concealedintheovule. The 
microspore contains vestiges of a 
minute prothallium. 
In the angiosperms the mega- 
spore and its prothallium are still 
less developed, and the micro- 
spore, or pollen grain, has lost 
all traces of a prothallium and 
is merely an antheridium which 
sooner or later produces two 
generative cells. These are most 
easily seen in the pollen grain, 
but sometimes they are plainly 
visible in the pollen tube (Fig. 
123, B). : 
Seed-plants are distinguished 
from all other plants by their 
power of producing seeds, or enclosed megasporangia with 
embryos. 
384. The Sexual Generation and Relationships of the 
Great Groups of Plants. — On summing up Sects. 381- 
383 it is evident that the sexual generation in general 
