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KIRKWOOD: POLLEN-FORMATION IN CUCURBITACEAE 223 
cells remaining undivided, in others giving rise to a considerable 
mass of pollen-mother-cells. 
In this study attention has been given to the development of 
the pollen in three species of the Cucurbitaceae representing as 
many genera. The forms studied are Fevillea cordifolia L., Mi- 
crampelis lobata (Michx.) Greene, and Cyclanthera explodens Naud. 
In Fevillea at the time when the anther begins to form the 
archesporium appears. At this time the anthers are rounded 
bodies, more or less flattened laterally by mutual contact. Growth 
takes place more rapidly in a radial direction, and a little later by 
reason of lateral pressure they become almost triangular in cross- 
Section. At the two angles of each anther on the periphery a 
group of cells retain their meristematic character while the rest 
become more vacuolated and react less strongly to stains. 
In the two outer angles of each anther a layer of cells contig- 
uous to the epidermis divides by periclinal walls, thus giving rise to 
the primary sporogenous and primary parietal cells. Both of these 
again undergo divisions. The parietal series gives rise to four 
layers of cells, so that the external wall of the anther early comes 
to consist of five layers of cells including the epidermis. In this 
region of the anther the greater number of sporogenous cells 
divide repeatedly so that an almost cylindrical mass of spore- 
mother-cells is developed in each angle of the anther. 
As usual, the layer of sterile cells adjoining the sporogenous 
tissue is developed as a tapetum and presents the usual appear- 
ance of such a tissue. The cells of this layer have two or more 
Nuclei each, and the size and chromatic content of these nuclei, as 
well as their deeply staining cytoplasm, mark them off in sharp 
Contrast from the adjoining sterile tissue. The tapetal cells retain 
their appearance of activity almost to the time of maturity of the 
pollen, : 
The usual process takes place in the formation of microspores. 
These are enclosed for some time in a somewhat gelatinous en- 
velope before they round off and develop the thick exine. The 
division of the nucleus of the spore takes place quite late if at all. 
Although almost mature anthers were sectioned, no case was 
found in which a microspore contained more than one nucleus. 
In Micrampelis several cells immediately below the epidermis 
