212 Sargant, — Formation of the Sexual Nuclei 
dehydrated in the usual way, cleared in clove-oil, and examined 
in xylol under a simple microscope. The lobes are separated, 
and those only are used which are well covered with pollen- 
grains. Sections are cut between slices of pith in a direction 
perpendicular to the cleft in the lobe, razor and material being 
kept wet with xylol. The sections are mounted at once in 
Canada-balsam, and examined with an immersion objective. 
It is easy to find pollen-tubes and germinating pollen-grains 
containing the generative nucleus in the spirem-condition 
without nucleolus or nuclear membrane, but later stages are 
rare. Some stigmas which had been cut and fixed between 
half-past one and two o’clock on a sunny day gave me the 
best results. 
Very soon after the pollen-grain reaches the stigma, the 
spirem-ribbon is differentiated in the generative nucleus. The 
vegetative nucleus continues in the resting-state (Fig. 30). 
The pollen-tube grows out at the place where, as we have 
already seen, there is a thin-walled stripe or gore in the exine 
(Figs. 30 and 30 a). It pushes downwards among the stigmatic 
hairs, on the top of which the pollen-grain rests. The tube 
twists over and round these hairs until it reaches their base 
and crawls between them. When the pollen-grain is thus 
firmly anchored to the stigma, its nuclei enter the tube, the 
vegetative nucleus usually going first 1 . Sometimes the upper 
end of the pollen-tube remains within the exine until the cell- 
contents have travelled away from both. In other cases the 
exine may fall off (as in Fig. 31), and the turgid pollen-tube 
stand nearly upright on the stigma (/. t. Fig. 31). The 
division of the generative nucleus is most easily observed 
when it takes place within such an up-standing tube (Figs. 32, 
33), or when, as sometimes happens, the pollen-grain has fallen 
on the very edge of the cleft down which it must plunge, so 
that its course is perfectly straight from the beginning. Very 
often, however, this division is postponed until both nuclei are 
creeping among the bases of the stigmatic hairs ; in that case, 
Guignard, 1 . c., p. 177. 
