SPERMATOPHYTES 
2 35 
antipodal region are multinucleate, and those of the micropylar region 
become so (two to five-nucleate). Since there is no uninucleate cell in 
the micropylar tissue, there is no archegonium initial, and hence no 
archegonium. Instead, several of the multinucleate cells develop what 
have been called prothallial tubes, which penetrate the overlying 
nucellar tissue, and into them the nuclei pass, each nucleus being a 
potential egg nucleus. It is at this point that the archegonium dis- 
appears ; which seems to be associated with the fact that the egg 
nuclei are differen- 
tiated before wall 
formation in the en- 
dosperm has been 
completed. 
Gnetum. In this 
genus there is free 
nuclear division as 
before, but wall for- 
mation does not oc- 
cur, so that the em- 
bryo sac at the time 
/, ..,. . 532 533 
of fertilization con- ,, . 
.FIGS. 532, 533. Male gametophyte of Ephedra: 532 
tains Only Iree nuclei pollen grain in shedding stage, containing two vegetative 
(fig. 531), and each nuclei (below), stalk (stri) and body (bn) nuclei, and tube 
one of these free nudeus ( above > 5 533, completed male gametophyte (after 
beginning of pollen tube), showing in the tube the male cells 
nuclei is a potential ( w ), sta lk nucleus (.?), and tube nudeus (0- After LAND. 
egg nucleus. This 
is the general angiosperm condition. Below the antipodal end of the 
sac a remarkable nutritive (glandular) tissue is developed. 
Male gametophyte. The male gametophyte of Gnetales is known 
only in Ephedra. In its shedding condition the pollen grain of 
Ephedra contains two persistent vegetative cells, and conspicuous 
stalk, body, and tube nuclei (fig. 532). In this condition the pollen 
grain rests on the exposed archegonium necks, and before the pollen 
tube is formed the body nucleus divides into two equal male nuclei 
( fi g- 533)- 
Fertilization. The phenomena of fertilization vary with the struc- 
ture of the female gametophyte. In Ephedra the pollen tube breaks 
through the long and massive neck of the archegonium (fig. 529); in 
Tumboa it conies into contact with the prothallial tubes that are pene- 
