20 THE FEUIT OF OPUNTIA FULGIDA. 



62 ) . Whether or not there is a preliminary softening of the cell-walls of the 

 abscission layer, there is evidently a change in the cell-walls of the vascular 

 bundles in the line of fission, as these become flabby and distorted before 

 abscission occurs (fig. 68). Mucilage cells lying in the line of fission are 

 usually not traversed by it, but cells within or without these become trans- 

 formed into abscission cells (figs. 61, 68). 



The lining of the funnel left at the top of the ovary after abscission is thus 

 made up, from the outer edge of the funnel dovm nearly to its bottom, of the 

 thin-walled cells derived from the abscission layer. Immediately after 

 abscission the outermost cells dry and shrivel (fig. 62), while cells just below 

 the surface begin the production of the protective layer of cork cells which 

 will be noted in describing the fruit (fig. 63). The very bottom of the 

 funnel left after abscission is in most cases formed by the short stump of the 

 style, which is ajjparently cut off by an irregiilar transverse rupture of the 

 cells without the formation of any distinct abscission layer. The wall of the 

 funnel for a millimeter just above the stump of the style is still lined by the 

 epidermis (fig. 24). Only in those cases where the abscission layer cuts 

 across below the base of the style (fig. 61) is the corky lining of the funnel 

 complete from the start. 



MORPHOLOGY OF THE OVARY. 



The flower of this species of Opuntia^ like that of any angiosperm, is to be 

 regarded as a branch of the shoot which bears carpels, stamens, petals, etc., 

 instead of the usual photosynthetic leaves, but it is unusual, or indeed almost 

 unique, in retaining a large series of the characteristics of the vegetative 

 shoot. This is indicated clearly by certain features of its earlier develop- 

 ment, by the occurrence on it of photosynthetic leaves with axillary buds, and 

 by tlie occasional presence on it of spines, like those of the vegetative shoot. 

 Further evidence tending in the same direction is offered by the persistence 

 and secondary growth of the fruit, by the vegetative multiplication of the 

 flower and fruit, and, finally, by the occurrence of many types of structures 

 intermediate between the typical fruit and the typical vegetative joint. In 

 this assemblage of peculiarities the flowers of this and certiiin allied 

 opuntias are unique, so far as I can learn from published records. In the 

 allied genus Peireskia the primary flower does, it is true, bear several pairs 

 of green leaves, with buds in their axils, and 2 or 3 of these may give rise to 

 secondary flowers. Tertiary flowers, however, are more rare, as far as I 

 have learned, and clusters of more than 3 or 4 mature fruits have not been 

 seen. I^o record has been found of these axillary buds of the ovary giving 

 rise (either before or after the separation of the fruits from the plant) to 

 vegetative shoots of the sort formed by fruits of Opuntia fulgida. In the 

 genus Cereus also something of the same kind evidently occurs at times. 

 Thus Harris (1905, p. 535) describes briefly the occurrence, in a specimen 

 of Cereus hoxaniensis, of " several terminal fruits, one of which had other 

 flowers developing from the side." A section of one of the (primary?) 



