De Life of the Plant. 
which still lies above it. 
189 
At the apex of the embryo-sac 
the pollen-tube comes into contact with the embryonic 
vesicles, and fertilises them (Figs. 361, 362). 
The exact 
mode in which this happens is not yet known, since at the 
time of fertilisation the pollen-tube, which is sometimes 
more, sometimes less considerably swollen, appears to con- 
tain no substance of definite 
structure. Immediately after 
fertilisation, the embryonic 
vesicles, which were before 
naked, become clothed with 
a cell-wall of cellulose, and 
begin at once to develope. 
It is indifferent whether one 
or both vesicles are fertil- 
ised ; one almost invariably 
perishes, perhaps 
want of sufficient nutri- 
ment, while the other un- 
dergoes further develop- 
ment, This divides, at first, 
into two cells, the upper 
one of which becomes the 
suspensor, while the lower 
one developes by frequent 
division and growth into the 
embryo (Fig. 363). The sus- 
pensor is sometimes longer, 
as in Borraginee, Cruciferze, 
Labiate, and  Scrophu- 
lariaceze, or shorter, as 
in Graminez, Irideze, Lilia- 
ceze, and Polygonacez ; in 
from. 
E 
Fic. 362.— Fertilisa- 
tion of Canna; I, 
apex of the embryo- 
sac é€ at the time 
when the _ pollen 
tube Zs has just 
come into’ contact 
with the embryonic 
vesicles &£; II. fer- 
tilised embryonic 
vesicle separated. 
(x 200.) 
Fic. 363. — Forma- 
tion of the embryo 
of  Aeliotropium ; 
e@ endosperm; e¢ 
suspensor; @ rudi- 
ment of the embryo, 
its enveloping mem- 
brane being already 
formed ; a cells de- 
veloped out of the. 
two embryonic vesi- 
cles: 
a few cases, as Cynanchum and Tropeolum, it swells up con- 
siderably, and is then called the pro-embryo, a term which 
should properly be applied to it in all cases. 
