SPERMATOPHYTES 
217 
FIG. 480. Male gametophyte 
of Dacrydium (one of the podo- 
carps) at shedding stage of pollen, 
showing four vegetative cells, stalk 
the 
tube 
nucleus. After Miss YOUNG. 
there is much nucellar tissue to be traversed before the female gameto- 
phyte with its archegonia is reached. For the first time, the pollen 
tube acts as a carrier of the male cells, the 
body cell, which is to divide, entering the 
tube and remaining near its tip as it ad- 
vances through the tip of the nucellus (fig. 
479). The tube may advance directly 
towards the archegonia or it may pursue a 
devious route, in some cases not reaching 
the archegonia until during the second 
season. When an archegonium is reached, 
its neck is broken through and the contents 
of the tip of the pollen tube are discharged 
into the egg (fig. 481). 
Embryo. In the development of the and bod y cells < formed 
, . generative cell), and the 
embryo from the fertilized egg, there is a 
variable amount of free nuclear division, 
from four free nuclei (Torreya, fig. 482) up to thirty-two, in strong 
contrast with the very numerous free nuclei appearing in the embry- 
. ogeny of cycads and of 
Ginkgo. After the free 
nuclei are formed, walls 
appear, and the resulting 
tissue (proembryo) fills the 
egg. In general, there are 
about three tiers of cells in 
the proembryo, the lowest 
(innermost) one usually con- 
sisting of a single cell, so 
that the proembryo has a 
general conical outline (fig. 
483). An elongation of cells 
begins in the upper (outer- 
most) tier (fig. 484), and 
this is continued by the 
middle tier, so that the 
FIG. 481. Fertilization of Torreya: the pollen terminal Cell, which is to 
tube has discharged its contents into the egg, and . , . , 
the male and female nuclei are f using. - After form the embryo, IS thrust 
COULTER and LAND. out of the archegonium and 
