KIRKWoop: POLLEN-FORMATION IN CUCURBITACEAE 231 
and other plants. On the other hand, the pollen-mother-cells of 
Equisetum™, Larix, Lilium, and Pisum show an entirely different 
condition of the cytoplasm in this respect. In these types the 
perinuclear zone does not exist and the origin of the achromatic 
figure is not so restricted. In several forms distinct fibers could be 
seen radiating from the nucleus toward the periphery of the cell 
and these fibers by folding over form a felted layer from which a 
multipolar spindle is later differentiated, and finally the multipolar 
spindle becomes bipolar by the fusion of the several poles into two. 
Allen‘ even suggests that this is a general process occurring in all 
spermatophytes. While this generalization seems not to be well 
founded, it does appear that we may generally refer the divisions 
of the spore-mother-cells in the higher plants to one type or the 
other. It has already been suggested (Cannon*) that the perinu- 
clear zone may inhibit the formation of the spindle in the periphe- 
ral cytoplasm as it occurs in Pisum. 
The process of mitosis as it occurs in Micrampelis presents 
Some features which distinguish it from most cases. It has been 
pointed out above that the cytoplasm assumes a radial structure 
as the time approaches for the first division of the spore-mother- 
cell. At the same time the separation of the plasmatic membrane 
from the cell-wall enables the cell to assume a spherical form. 
The contraction of the cytoplasm is accompanied by the contrac- 
tion of the nucleus so that the latter becomes angular and exceed- 
ingly distorted. Up to this time no special differentiation of the 
cytoplasm can be detected, but soon a few fibers can be seen run- 
ning more or less parallel with the nuclear membrane; here they 
form a very thin reticular layer. While this change is taking 
place in the cytoplasm the nuclear structures are also changing. 
The chromatin is collecting into chromosomes and the linin ap- 
pears as an almost colorless network of fine fibers which run in all 
directions. At this time the cytoplasm adjoining the nucleus 
Stains a little more darkly than the rest, and as the nuclear wall 
dissolves, pencils of fine fibers may be seen pushing out from the 
Nucleus into the surrounding cytoplasm. These bundles of fibers 
Originate from the reticulum adjoining the nucleus. Soon the 
bers are seen traversing the nuclear vacuole, which rapidly dig- 
4ppears and several poles project out from the nuclear position. 
