Division of the Generative Nucleus in Pines. 205 
presence in the pollen-tube of large quantities of starch 
(Fig. 20). This starch, which resists the microtome knife 
and is therefore easily displaced by it, not infrequently falls 
out and carries away with it the free cells of the pollen-tube. 
The dead, deeply staining tissue of the nucellus, representing 
that portion of the nucellar cap which was penetrated by the 
pollen-tube during the previous season, and in which the 
generative cell divides (Fig. 4), is also very troublesome. 
Furthermore the dense cytoplasm of the generative cell shows 
a great affinity for stains, so that when the archegonia and 
other portions of the ovule are well stained, this cell often 
appears merely as a deeply stained mass of no significance. 
Considering these facts, it is not surprising that seven hundred 
slides of serial sections were made, which means that more 
than two thousand pollen- tubes were studied, before any 
definite clue was obtained as to the true sequence of events 
in the development of the pollen-tube. When once the 
mitotic figure was observed in the pollen-tube , scarcely more 
than a week before fertilization, and the fact noted that 
special staining was necessary in order to study this mitosis 
satisfactorily, further research was prosecuted with compara- 
tive ease. 
After the generative cell has passed into the pollen-grain, 
but while it is still in the upper dead portion of the nucellus, 
it gives rise to the sperm-nuclei by a division which presents 
some new and interesting features, while it resembles to a 
greater or less degree certain mitoses described by various 
cytologists 1 during the past few years. 
When the generative nucleus has again come to lie in 
1 Of the long list which might be mentioned I have noted only the following : 
Guignard (’91) in the embryo-sac of Lilium ; Rosen (’95) in the root-tip of 
Hyacinth; Osterhout (’97) in Equisetum ; Swingle (’97) Sphacelariaceae ; Schaff- 
ner (’98) in root-tip of Allium Cepa ; Mottier (’98) in the embryo-sac of Lilium ; 
Fulmer (’98) in pine seedlings; Hof (’98) in Ephedra and other plants; Nemec 
(’98 and ’99) in various plants; Strasburger (’00) in Vicia Faba , and Mottier 
(’00) in Dictyota. Of animal-cytologists I will mention but one : Hertwig, R., 
(’98) in Actinosphaerium. This division in Actinosphaerium bears in certain 
stages of its prophase a most striking resemblance to an early prophase of the 
mitosis about to be described. 
