207 
Beer. — Studies in Spore Development . 
to spread out irregularly into the interior of the protoplast (Fig. 12). It has 
the appearance of a material, derived from without, which is making its 
entrance through the exit pores of the pollen-wall, which is then taken 
up by the little pseudo-podium-like processes of the protoplast, and which 
from these points becomes diffused through the cytoplasm of the pollen- 
grain. I have been able to obtain but little information with regard to the 
chemical nature of this substance. From the fact that it is blackened by 
the osmic acid in Flemming’s solution it is probable that the material is of 
a fatty nature, but beyond this I can say nothing at present. 
It may be noted that just about the time when this dark-coloured 
material is making its appearance in the pollen-protoplast, a number of 
vacuoles of varying sizes are formed in the tapetal cells, and that these 
vacuoles are filled with a material which is also darkened by osmic acid. 
I have not succeeded in tracing this darkened material out of the tapetal 
cells into the cavity of the anther and establishing a direct connexion with 
the similarly blackened substance in the pollen-protoplast, but such a rela- 
tionship between the two appears quite likely. Moreover, the tapetal cells 
can be seen to undergo a loss in the total amount of substance they contain. 
These facts taken together suggest that the pollen-protoplasts are growing 
and storing reserve bodies in their substance at the expense of materials 
derived, at any rate in part, from the tapetal cells. During the earlier stages 
of the growth of the pollen-protoplast we find that its nucleus divides, and 
that the very unequal cell-division which follows cuts off a small generative 
cell from the large tube cell. The cytoplasm of the generative cell is 
almost entirely composed of kinoplasmic fibres radiating from its nucleus 
(Fig. 13). In older generative cells the fibrillar constitution of the cytoplasm 
gives place to a dense, almost hyaline structure. 
A distinct plasma membrane limits the generative cell peripherally, but 
no cell-wall is developed (Fig. 14). The nucleus of the generative cell 
measures about 14 ju, in diameter, and contains a comparatively large 
nucleolus and a rather loosely arranged system of fibres. 
The tube nucleus is large, irregular, or even amoeboid in outline, and is 
distinguished by the enormous nucleolus and the system of deeply staining 
chromatic threads which it contains (Fig. 15). Amoeboid tube nuclei have 
been described in a number of other plants ; for instance, in Elodea canadensis 
by Wylie ( 22 ). 
The nucleolus of the tube nucleus is surrounded by a sheath of 
chromatin, and there are here no signs of the clear space ( heller Hof ) between 
the nucleolus and the chromatic reticulum of the nucleus which several 
writers have described (Fig. 15). In such cases as that represented in 
Fig. 1 6, where a slight contraction of the nucleolar substance has taken 
place at one spot, the relation between the nucleolar material and the 
chromatic sheath is particularly well seen. Martin Heidenhain, as long ago 
