12 THE FRUIT OF OPUNTIA FULGIDA. 



The facts and structures of interest in connection with these areoles are: 

 their number and distribution, the origin of the growing-point, the trich- 

 omes, the nectaries, the spines, and the bristles or spicules. 



NUMBER. SIZE, AND DISTRIBUTION OF THE AREOLES. 



Since there is a bud in the axil of each of the leaves of the wall of the 

 ovarj, except in the cases of 4 or 5 of the upper ones tkat are appressed 

 against the sepals, the total number of areoles formed is nearly the same as 

 that of the leaves. Mature ovaries show from 15 to 35 or (in joint-fruits) 

 even 40 areoles. But these are not by any means alike in size or in. the 

 number of organs or organ rudiments present in them. The size varies 

 from 1.5 to 3 mm. in diameter in flowers just opening, while the areoles of a 

 three-year old fruit may become 4 or 5 mm. broad by 6 or 8 mm. long ( figs, 

 4, 8, 47, 49). The areoles of the upper third of the fruit are in general 

 larger and more complexly organized, while those of the lower third are 

 usually much smaller and of very simple structure. The former are the 

 ones most likely, under satisfactory conditions, to develop further. The 

 lower ones usually grow little after the maturing of the fruit. They gTa du- 

 ally become depressed more and more deeply into the surface of the fruit, 

 till they are nearly buried from sight. The lower half-dozen areoles have 

 never been seen to give rise to either flowers or vegetative branches. Tn a 

 fallen fruit, however, adventitious roots may push out the upper border of 

 such a dormant or apparently dead areole (fig. 100). 



As seen from without, the mature areole appears as a grayish yellow, 

 bulging cushion, of circular or somewhat longitudinally elongated outline 

 (figs. 4, 8, 47). The surface of this cushion is made up of the ends of 

 hundreds of spirally striated trichomes, which at first surround and overtop 

 all other rudiments in the areole. In slightly advanced areoles dozens or 

 scores of straight, barbed bristles or glochidia push from beside or beneath 

 the tuft of trichomes in the apical half of the areole. ITear the middle of 

 such a cushion may be seen the flattish tops of one or several spine-tipped 

 nectaries (figs. 14, 47, 48, 49, 50). Still later, in certain of the areoles of 

 the upper third of the ovary, the tip of the bud of a secondary flower may be 

 seen. This is at first covered by a protecting lattice made up of the peg-like 

 leaves, which push out of the cushion of trichomes, just below the crescentic 

 group of spicules and just above the nectary or nectaries of the areole (figs. 

 13, 15, 47). In the lower areoles of some of the more elongated fruits one 

 or two spines may be formed which resemble those found in the areoles of the 

 vegetative joints, but are usually weaker (figs. 13, 28). 



ORIGIN OF THE GROWING-POINT OF THE AREOLE AND THE ORDER OF 

 INITIATION OF ITS ORGANS. 



The growing-point of the areole becomes distinguishable at a time when 

 the subtending leaf has attained less than a quarter of its mature length; 

 that is, when it is only 0.5 mm. long. It at first consists of a very small 



