14 THE FRUIT OF OPUNTIA FULGIDA. 



There can be no donbt that these trichomes serve to protect from des- 

 iccation the growing-point of the areole and the young rudiments formed by 

 it. In other words, they sei've the function served by bud-scales, or modi- 

 fied leaves, in the axillary buds of most woody plants. The number and 

 length of these trichomes enables them completely to submerge all other 

 structures in the bud except the nectaries and the full-grown spicules. The 

 latter protrude for half their length, while the flat ends of the former can be 

 seen in surface view of the areole, each with, a densely packed ring of 

 trichomes about it that have been crowded aside by the swelling of the 

 nectary. These clustered trichomes make a more efl:"ective protection also 

 because of the enlarged, thick-walled cells at the end of each of them. The 

 lattice-like thickening of these cells enables them to maintain their form and 

 full size when dried out completely by the desiccating winds of their native 

 habitat. Whether the trichomes have other functions at any other period 

 of their existence has not been detennined. None has suggested itself to 

 the writer as probable in the course of this study. 



The final fate of these trichomes has been suggested by what was said of 

 the breaking-off of the terminal cells. This process is apparently repeated 

 until the trichome practically disappears ; at least, the older areoles contain 

 large numbers of decapitated hairs, many of them with only a few of the 

 basal cells left. 



NECTARIES OF THE AREOLE : THEIR DISTRIBUTION AND MORPHOLOGY. 



In every areole, soon after the difi^erentiation of its growing-point and the 

 development of a few score of trichomes, there appears among the latter, on 

 the side of the growing-point toward the leaf, the rudiment of a nectary. 

 In many of the smaller, basal areoles of the fruit only one or two of these 

 nectaries may be formed, and these lie close to the sagittal plane of the 

 areole (figs. 24, 47). In the larger, upper areoles, however, the number of 

 nectaries may continue to increase with the growth of the areole until, by the 

 end of the first growing-season, there may be 8 or 10 nectaries present in, 

 each (figs. 5, 47, 48, 49). As the areole grows year after year on the per- 

 sistent fruit, the number of living and withered nectaries may continue to 

 increase till 20 or more have been formed. Not more than 4 or 5 mature, 

 living nectaries are present at one time, but a number of younger ones may 

 be initiated between a mature one and the groAving-point before this begins 

 to shrivel. In the upper areoles of a primary ovary secondary flower-buds 

 usually appear after but 2 or 3 nectaries have been developed, and these are 

 soon crowded aside to wither as the secondary bud swells (figs. 47, 49). In 

 case secondarv flowers are not formed from an areole until the second or a 

 later year, there may be many old nectaries found crowded aside or partially 

 crushed by the stalk of the enlarging secondary fruit (fig. 14). These nec- 

 taries were evidently initiated before the flower, since the latter, as we have 

 seen, involves the whole growing-point of the areole (fig's. 10, 12, 14). 



