28 THE FRUIT OF OPUNTIA FULGIDA. 



character and contents of the ovarian cavity. The main vascular bundles of 

 the wall increase only moderately after the fall of the perianth, though they 

 do increase somewhat in radial dimensions by the addition of new layers of 

 xylem tissues (fig. 44&). The amount of the cortical parenchyma outside 

 the vascular bundles may also increase somewhat, and this latter growth is 

 probably the cause of the rounding out of the fruit and the disappearance of 

 the mammillse (figs. 3, 76, 8). 



The number and character of the seeds present in different fruits differ 

 markedly. There may sometimes be an ovarian cavity filling three-fifths of 

 the diameter of the fruit, or this cavity may be practically wanting. About 

 half the mature fruits contain one or more ripe seeds, which vary in number 

 from 1 to 100 or 200 per fruit. The other half of the fruits have only small 

 ovarian cavities in which the seed rudiments have ceased their development 

 at different stages from half-formed ovules up to half -grown seeds (fig. 23). 

 In some cases not even these withered rudiments can be found in the place 

 where the ovarian cavity should be. 



A consideration of the facts related inclines at first to the conclusion that 

 ovaries mature into fruits only when pollination has occurred and that seeds 

 form only when the further process of fertilization has taken place. This 

 seems doubtful, however, in view of the fact that many seeds may go half- 

 way through their development before degeneration sets in. The attempt is 

 being made to determine the distribution of these different types of degenera- 

 tion in different plants and different flowers of the same plant. 



The most striking peculiarity of these mature fruits is that they do not 

 ripen. From analogy with all other fruits, we should expect at this time 

 that the flesh of the Opuntia fruit would either change color and soften or 

 harden up to form a dry fruit. But nothing of this sort happens. The 

 matured fruit, with its color still bright green, with its photosynthetic tissues 

 still active in starch-making, and its well-established fascicular cambium 

 simply halted until the next spring, enters into the resting-period of 4 or 5 

 months. There is not the slightest sign of ripening or any change at all 

 comparable with this process. There is no preparation of any sort for the 

 discharge or escape of the seeds to conditions conducive to germination. 

 On the contrary, the majority of the mature fruits normally remain attached 

 to the parent shoot, not merely through the succeeding fall and winter, but 

 season after season for several or many years. These persistent fruits 

 become essentially a part of the vegetative shoot, performing not only the 

 photosynthetic function of a vegetative joint, but also budding out new 

 shoots. Usually these shoots arising from attached fruits are floral shoots. 

 More rarely a vegetative joint may arise from such a fruit, and then the 

 latter becomes a constitutent joint of the vegetative branch, undistingiTish- 

 able except by its perianth-scar and usually by its lack of spines (fig. 79). 

 The fate of a fruit in these respects is the same, whether it contains many 

 fertile seeds or whether, as may often be the case, it is entirely seedless. 



