THE FRUIT OF OPUNTIA FULGIDA. 35 



PROLIFERATION OF FLOWERS AND FRUITS. 



The most unique peculiarity of the flower or fruit of Opuntia fulgida is 

 its ability to produce new shoots. These shoots may be floral shoots only, 

 as in the case of the attached flower or fruit, or they may be vegetative shoots, 

 as in the case of detached fruit. This capacity for proliferation is depend- 

 ent, as has been noted, on the presence and persistence of the axillary buds or 

 areoles of the wall of the ovary. These axillary buds are unknown, as far as 

 the writer has been able to leam, on the ovary of any other family of plants, 

 and even in the Cactacese occur only in the genera Opuntia, Nopalea, and 

 Peireskia. 



The structure of these areoles, with a description of the rudiments present 

 in them, has already been noted (p. 11). We have seen also that most 

 of the areoles of a flow^er and fruit may persist year after year without 

 developing anything but minor organs,- such as nectaries, trichomes, and 

 spicules. We have now to consider the very important function perfoiined 

 by certain of the areoles in their proliferation to shoots of limited or 

 unlimited growth. There are three types of proliferation by the areoles of 

 the ovary of this opuntia. In the first place, from 1 to 5 or more of the 

 areoles of the unopened flower may give rise to the buds of secondary flowers, 

 which open soon after the primary ones. Secondly, one or several areoles of 

 an attached fruit may in the first or in some later season after its develop- 

 ment give rise to primary flowers of that season. Thirdly, the areoles of a 

 detached fruit that has been separated from the parent plant after maturing 

 and placed on moist soil may give rise, first to adventitious roots and then 

 later to the characteristic joints of vegetative shoots. The fruit thus per- 

 forms the unique function of initiating a new plant by purely vegetative 

 propagation. 



PROLIFERATION FROM ATTACHED FLOWER BUDS. 



The primary flowers of the season arise in either April or May on either 

 the vegetative joints or the fruits of the preceding season or sometimes on 

 those of a still earlier season. These flowers are developed from the growing- 

 points of the upper areoles of the joint or fniit (fig. 47) in the manner noted 

 above (p. 9). 



Before the primary flower is half-grown the buds of secondary flowers of 

 various sizes can be detected developing in from 1 to 4 or 5 of its upper 

 areoles (figs, ^a, 9&, 13). By the time the primai-y flower is ready to open, 

 soon after the middle of May at Tucson, the larger buds of the secondary 

 flowers are about one-sixth grown, and are recognizable as buds of flowers 

 rather than of vegetative shoots (figs. 9a, 9&, 47). About 4 weeks after the 

 primary flower withers and sheds its perianth, the largest secondary flower in 

 its turn opens. This occurs usually between the middle and end of June, 

 and the buds of the tertiary flow^ers are then already well developed in their 



