18 THE FRUIT OF OPUNTIA FULGIDA. 



oped ; that is, when there are 6 or 7 stamens, one above the other, on one side 

 of the growing-point in a single radial longitudinal section (fig. 18). The 

 carpel rudiment at its initiation is twice as thick as that of a stamen. It 

 differs, also, in that it almost immediately bends inward above the growing- 

 point to meet its fellows and thus to complete the roof of the ovarian cavity 

 (figs. IT, 18, 19). Soon after the tips of the carpels meet they begin to fuse 

 together along their radial surfaces to form the rather stout style, which 

 incloses a papilla-lined stylar canal, that is star-shaped in cross-section (figs. 

 21, 23, 35, 37). The very tips of the carpels, for a length of 3 or 4 times their 

 diameter, remain unfused and form the stigmatic lobes. These finally 

 become 1 to 1.5 mm. long and are densely clothed with swollen, sac-like 

 hairs that serve for the attachment of pollen-grains (figs. 23, 36). Begin- 

 ning at a depth of 5 or 6 layers inward from the wall of the stylar canal is a 

 corrugated tube of conducting tissue 8 to 20 or even 30 cells in thickness, 

 through which the pollen-tube is to push its way (figs. 22, 34, 35). The 

 slender cells of this conducting layer extend upward to the very base of the 

 hairs of the pollen-receiving surface of the stigma (fig. 36). At the base of 

 the style this layer is continued downward as a series of strands reaching to 

 the roof of the ovary (figs. 22, 23, 24). The mature stigma lobes are con- 

 tinued outward and downward to form the characteristic 6-rayed or 7-rayed 

 structure seen in the open flower (figs. 30, 31). The lining of this part 

 of the ovary wall, down to the uppermost ovules, is covered by slender hairs 

 protruding into the cavity of the ovary. These probably help to conduct the 

 pollen-tubes to the micropyles. 



Wot only do the carpellary lobes, which are at first transverse, grow 

 upward after meeting above the depressed growing-point, but they may 

 also often grow downward somewhat into the ovarian cavity, thus making 

 the roof of the latter lowest near the center (figs. 11, 21, 61). Transverse 

 sections of the ovary at this time may show several upward prolongations of 

 the ovarian cavity, separated from each other by the downward growth of 

 the carpels at the plane of juncture of the two carpels of each pair. The 

 impression given by such a section is that of a compound ovary with 6 or 7 

 separate cavities. 



The separation and fall of the perianth, and other parts that fall with it, 

 is a complicated and rather variable process, as compared with the shedding 

 of parts in most choripetalous flowers. In about 3 days after the flower has 

 opened the withering of the sepals and petals has gone so far that all those 

 of a flower are twisted together into a cone of dry, crisp remnants ; that is, 

 the parts of the flower do not drop off individually, as usually happens in 

 choripetalous angiosperms, but the whole series of sepals, petals, stamens, 

 and in some cases even the style, are cast off from the ovary at once, all 

 attached to a cup-like common base stripped off from the upper end of the 

 ovary. This wholesale shedding of the floral parts is accomplished by the 

 formation of a highly developed abscission layer across the entire upper end 



