Division of the Generative Nucleus in Pines. 213 
The formation of the sperm-nuclei shows very beautifully 
the development of the nuclear reticulum. The chromosomes 
unite end to end, giving rise to a homogeneous, coiled band, 
before the nuclear membrane is formed. When the nuclear 
wall has been differentiated, the coil expands about the peri- 
phery of the nucleus and the band broadens, at the same time 
becoming irregularly jagged along its margins. These irregu- 
larities increase in length until finally those from neighbouring 
portions of the thread meet and fuse, thus giving rise to the 
reticulum (Figs. 37-40). 
When the two sperm-nuclei have nearly or quite come 
into contact they have as a rule reached their mature size. 
More than a year has now elapsed since pollination. Up to 
this time the pollen-tube has elongated very slowly, having 
penetrated as yet little, beyond the nucellar tissue of the 
previous year’s growth. In this upper portion of the nucellar 
cap the tube may become very broad or it may branch freely 
(Figs. 3, 4, 12, and 16). When the sperm-nuclei have at- 
tained their full size the downward growth of the tube is 
exceedingly rapid, as shown by Dixon, and the tube is un- 
branched and comparatively straight (Fig. 5). In Pinus Stro - 
bus and P. austriaca about ten days intervene between the 
division of the generative nucleus and fertilization ; in Pmus 
montana , var. uncinata , the two processes are separated by an 
even shorter space of time. 
The sperm-nuclei which at first present a very beautiful, 
rather delicate reticulum (Figs. 47 and 48), become more dense 
as the pollen-tube advances through the nucellus. Stras- 
burger (’ 92 ) describes them as coarsely granular, but, with 
a high power, the presence of a reticulum which is sometimes 
coarse and interrupted can invariably be made out in well- 
prepared material. By the time that these nuclei have reached 
the central portion of the nucellar cap they have usually 
become very dense in structure (Figs. 46 and 46 b), and 
frequently stain intensely, though they may show at this time 
a weak reaction to dyes. The reticula of the two nuclei 
may present the same appearance, or they may differ as in 
