SPERMATOPHYTA 
405 
degenerate, while the remaining one germinates (Fig. 452) and 
produces a female gametophyte, or prothallus, which remains per- 
manently inclosed within the sporangium 
(Fig. 453). In most of the gymnosperms 
archegonia are produced at the micropylar 
end of the prothallus, but in the angio- 
sperms there are no archegonia and one of 
the cells of the prothallus becomes an egg. 
Microsporangia and microspores. ‘The mi- 
crospores (pollen grains) are borne in micro- 
sporangia on microsporophylls (Figs. 296, 

Fig. 453. Somewhat 
diagrammatic longitu- 
dinal section of meg- 
asporangium of pine, 
containing a female 
prothallus with two 
archegonia 
m, micropyle ; i, integu- 
ment; n, nucellus; p, 
pollen tube; e, egg in 
archegonium ; f, female 
prothallus. (x 14) 
481), which in the an- 
giosperms are called 
stamens. In the gym- 
nosperms the micro- 
spores are carried by 
the and by 
chance some are de- 
posited at or in the 
micropyle (Fig. 451) 
of a megasporangium 
(ovule). The micro- 
spore sends out a pol- 
len tube that grows 
through the nucellus 
toward the archego- 
nia (Fig. 453). The 
eggs in the arche- 
gonia are. fertilized 
either by spermato- 
zoids or by male 
wind, 
nuclei from the pollen tube. In the angio- 
sperms, where the megasporangia (ovules) 
are inclosed in an ovary, the microspores are deposited on the 
stigma, and the pollen tube grows through the style before 
reaching the megasporangium (Fig. 4). 

Fria. 454. Longitudinal 
section of pine seed con- 
sisting of the embryo 
surrounded by the fe- 
male prothallus and this 
in turn by the seed coat 
formed from the integu- 
ment. (<5) 
