KiRKWooD: POLLEN-FORMATION IN CUCURBITACEAE 235 
thick, and irregular masses (FIGURE 42). As this change is taking 
place the nuclear wall is becoming irregular and. the incipient 
stages of spindle-formation appear in the cytoplasm. The evidence 
of true tetrad formation is not very abundant at this point, but in 
certain cases a double division of the chromosomes appeared to be 
quite clear (FIGURES 43, 44). The chromosomes at this stage be- 
come so nearly isodiametrical that it becomes practically impossible 
to distinguish between a longitudinal and a transverse division of 
the chromosome. 
The first division is clearly of heterotypic form. The chromo- 
somes appear united in the form of rings in the metaphase of the 
division (FIGURES 46, 47). The spindle fibers are attached to oppo- 
site sides of the ring and the separation takes place midway between 
the points of attachment of the spindle-fibers. The relation of the 
chromosomes to the fibers appears in FIGURE 50. After the separ- 
ation of the chromosomes in the early anaphase of the division they 
round off into almost spherical bodies to which are attached certain 
bundles of spindle-fibers. In a transverse section of the spindle 
these can readily be seen and correspond in number to the chro- 
mosomes. The chromosomes during the anaphase can be readily 
counted and number sixteen (FIGURES 51, 52), a number found by 
Strasburger® and Guignard '' in certain orchids. Owing to their 
minute size and the compact condition of the mitotic figure in the 
vegetative cells the number of chromosomes could not be deter- 
mined, but it appears to be easily more than sixteen. 
As the chromosomes draw closer together toward the apex of 
the spindle they become crowded together and lose their identity, 
So that as the daughter-nuclei are organized in the telophase they 
can no longer be distinguished from one another. They present 
the appearance of having become fused into a spireme (FIGURES 53, 
54), which finally resolves itself into a reticulum, with a tendency 
toward pairing of the most conspicuous chromatin masses (FIGURE 
55). This appearance is only transient, however, as the nucleus 
Passes quickly into the prophase of the second division, when the 
chromatin appears in dense masses, at first angular and connected 
With many radiating fibers (FIGURE 56), later rounded off and periph- 
frally disposed in the nuclear vacuole (FIGURES 57, 58). 
The second division shows a thick mass of chromatin on a 
