230 KirKwoop: POLLEN-FORMATION IN CUCURBITACEAE 
straying out into the cytoplasm from the poles of the spindle, and 
seem to be in contact with the dark bodies scattered through it, and 
when at the conclusion of the division the contracting mantle-fibers 
have drawn the chromosomes to the poles and the daughter-nuclet 
have organized, the wandering fibers have also disappeared and the 
dark bodies have assembled about the nuclei. Hither, however, 
they may have been carried passively, as there is a congestion of 
the granular cytoplasm about the daughter-nuclei, leaving a com- 
paratively clear broad zone across the equator of the spindle 
through which the division of the cytoplasm ultimately takes place. 
With the organization of the tetrads the cytoplasm undergoes 
a change and instead of appearing fibrillar it begins to assume an 
alveolar aspect. It is during this stage that the activity of the cell 
is directed mainly toward the differentiation of the spore and the 
storage of a food reserve, which would, of course, account for the 
predominance of trophoplasm and the relatively slight quantity of 
kinoplasm present. As the spore enlarges the cytoplasm is dis- 
tributed about its wall and only as it nears maturity does the 
central vacuole entirely disappear. The spore then becomes filled 
with granular proteinaceous matter. The differentiation of the 
exine begins while the tetrads are still clinging together, and is 
first evident by a thickening at the points where the germinal 
pores are afterwards to appear. In the mature spores, as usual, 
these are the thinnest places in the exine. The dark cytoplasmic 
bodies usually become segregated into some part of the spore as 
it approaches maturity and the cytoplasm in their vicinity usually 
stains more darkly than elsewhere. 
Great interest centers in the behavior of the kinoplasm during 
the process of cell-division, and Strasburger™ has given careful . 
consideration to the various expressions of its activity, showing 
that-it is concerned not only with the development of the spindle 
but also with the formation of plasmatic membranes. The pre 
dominance of kinoplasm over trophoplasm is one of the most con- 
spicuous features of the spore-mother-cells of plants, and this 
may appear in a variety of ways. In certain cases a distinct peri- 
nuclear zone appears just before the first division and stains very 
darkly, and from the fibers of this zone and the linin of the nucleus 
the spindle is formed, as in Cobaea'®, Lavatera®, Cassia", Gossypium 
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