2 12 Ferguson. — Development of the Pollen-tube and the 
vary with the shape of the pollen-tube. Gradually the two 
nuclei approach each other until they come to lie in the 
extreme uppermost part of their cytoplasm (Figs. 47 and 48). 
There is now considerable difference in their size. This in- 
equality in size could be detected as far back as the formation 
of the daughter-nuclei (Figs. 39 and 40). Coulter (’ 97 ) de- 
scribed two sperm-cells which were of the same size until 
within the archegonium. Blackman (’ 98 ) stated that each 
sperm-nucleus was clearly seen in the pollen-tube surrounded 
by its own cytoplasm, but he did not figure them. Chamber- 
lain (’ 99 ) figured the sperm-nuclei, in Pinus Laricio , of equal 
size in the pollen-tube, and showed them lying together in the 
cytoplasm of the tube. Not having seen these cells within 
the archegonium before the conjugation of the sexual nuclei, 
he accepted Coulter’s statement for the growth of one of them 
after their entrance into the egg. Two sperm-cells have not 
been observed in any of the pines which I have studied ; but 
the sperm-nuclei, which are of unequal size from a very early 
date, remain surrounded by a common cytoplasmic body 
(Figs. 39-50). As Strasburger (’ 92 ) observed, the larger 
nucleus is always ahead, that is, on the side nearest the apex 
of the pollen-tube. The smaller nucleus remains close against 
the upper boundary of the cytoplasm and suggests the condi- 
tion in Cycas (Ikeno, ’ 98 ) and Ginkgo (Hirase, ’ 98 ) where the 
stalk-nucleus is forced entirely out of the cytoplasm sur- 
rounding the generative nucleus. In this case the action is 
not carried to so great an extent. 
Only once has the smaller sperm-nucleus been observed in 
advance of the larger (Fig. 44). Here it will be seen that the 
entire order of arrangement has been changed and the stalk- cell 
and the vegetative nucleus are above the sperm-nuclei. But this 
abnormal arrangement is only apparent, for it was found that 
the egg which had been approached by this pollen-tube had 
already been fertilized, and the pollen-tube had turned aside 
and was passing up over the top of the endosperm. The position 
of the various elements of the pollen-tube is therefore normal, 
and the larger sperm -cell is in reality in advance of the smaller. 
