26 THE FRUIT OF OPUNTIA FULGIDA. 



atelj ventilated, photosjntlietic palisade of the cortex, with its scattered 

 slime-cells and crystal cells, and the complexly reticulated vascular system ; 

 and, finally, within the latter and between its meshes are many layers of 

 mucilaginous storage parenchyma. The latter in turn surrounds the cavity 

 of the ovary, now nearly filled by the young seeds and by the mass of loose 

 tissue arising from their long, coiled, funicular strands (figs. 23, 40, 71). 



The somewhat uneven outer layer of the epidermis of the projecting 

 tubercles consists at this stage of rather cuboidal cells, with bulging and 

 considerably thickened outer walls (fig. 71). The epidermal cells of the 

 grooves between the tubercles are somewhat elongated radially and thinner- 

 walled than those of the outer margins of the tubercles just described. 

 Stomata are scattered rather frequently over the surface of the tubercles. 

 The guard-cells are already sunken considerably below the surface, though 

 not as far as in the mature fruit (figs. 71, 72). The inner layer of the epi- 

 dermis already includes many crystal-containing cells of the sort figured in 

 detail in the older fruit (fig. 71, 72, 73). 



The cork of the fruit at this stage is confined to the pit-like scar at the 

 top of the fruit, where it forms an ashy-white layer. It consists, outside the 

 phellogen, of above 8 to 10 layers of rectangular cells approximately 100 

 microns long and broad and 20 to 40 microns thick, radially. The walls of 

 all save one layer of these are not greatly thickened, nor apparently strongly 

 suberized (fig. 63). The very bottom of this cup around the stump of the 

 style is commonly still protected only by the original epidermis, which, as 

 was noted earlier, is often not cast off along with that part of the lining of the 

 cup which bears the stamens (figs. 23, 60). 



The photosynthetic tissue of the ovary-wall has already begim to assume 

 the striking arrangement in radial rows that is so characteristic of the 

 cortical tissue of the mature fruit as well as of the vegetative joint (figs. 39, 

 70, 71, 73). Scattered abundantly through this palisade, which extends 

 inward 8 or 10 cells from the surface, are numerous mucilage-cells of the 

 usual more rounded form. 



The vascular-bundle system of the young fruit consists of about 16 pri- 

 mary bundles entering it at the base. These soon divide by dichotomous 

 forking to form twice as many bundles at the level of the lower end of the 

 ovarian cavity. The repetition of this forking gives rise in the upper half 

 of the fruit to a still more complex system of main vascular bundles (figs. 

 17, 21, 25,26). From the points of forking of these main bundles are given 

 off the groups of smaller bundles, one group at the base of each tubercle, to 

 supply the tubercle, its growing-point, and the leaf and nectaries arising 

 from it (figs. 21, 27, 28, 32). The main vascular bundles are nearly isodia- 

 metric in cross-section at this stage of development, and are about 500 

 microns thick radially and 300 microns broad tangentially (fig. 44a). In 

 internal structure, which may be noted briefly for comparison with the 

 bundle of the older fruit, each main bundle includes about 25 or 30 tangen- 



