THE FRUIT OF OPUNTIA FULGIDA. 9 



REPRODUCTIVE ORGANS OF OPUNTIA FULGIDA. 



The reproductive structures (flower, fruit, and seed) to which most atten- 

 tion has been paid in this study, will be described in some detail under three 

 captions: (1) the origin and structure of the flower; (2) the fruit, its 

 stinicture, persistence, and fate, normal and abnormal; (3) the seed, its 

 structure, persistence, and germination. 



The most aberrant features of the development of these reproductive 

 organs are : the structure of the Avail of the submerged ovary, with its numer- 

 ous axillary buds ; the capacity of these buds to initiate secondary flowers, 

 either immediately before the primary ones are open or later, in the same or 

 succeeding seasons ; and finally the ability of these same axillary buds, when 

 the fruit is detached, to form adventitious roots and shoots and thus to 

 initiate new plants. 



ORIGIN AND STRUCTURE OF THE FLOWER. 



The primary flower of the season in Opuntia fiilgida arises from one of 

 the upper or more terminal axillary buds or areoles of a last year's vegetative 

 joint or from an areole of a fruit of the first, second, or third year preceding. 

 The number of flowers develoj^ed on any one joint or fruit in a single season 

 ranges from 1 to 5 or more (figs. 4, 9a). In the case of the fruits, flowers 

 may be formed from other areoles in succeeding years until as many as 10 

 or 12 flowers and fruits are often found attached to a single persistent fruit 

 (fig. 48). The primary flowers of a season are first evident, in 0. fulgida 

 growing near Tucson, during the latter half of April. Open flowers are 

 rarely seen before the middle of May. The first flowers to appear and to 

 open are those developed on vegetative branches. In early May 1912, the 

 larger flower-buds on vegetative branches of one plant observed were 21 mm. 

 long, while the longest ones on a persistent fruit of the same plant were but 

 7 mm. ISTew flowers continue to open successively all through the summer 

 up to the middle of September. (See Toumey, 1898 ; Lloyd, 1907). 



DEVELOPMENT OF THE WALL OF THE OVARY WITH ITS TUBERCLES. 



The very young flower-bud, when firet pushing out of the tuft of trichomes 

 and spicules of the areole, is a rather hemispherical body about 0.3 mm. 

 in diameter. Its dome-like or somewhat conical upper end is formed by the 

 few earlier of the 15 to 30 or sometimes 40 leaves that are finally developed 

 from the wall of each ovary (figs. 4, 9a, 47). These leaves, when first 

 formed, arch over the dome-shaped growing-point (figs. 13, 14). As the 

 flower grows, the earlier leaves are pushed outward by the yoimger on^ 

 arising between them (figs. 17, 22). The axis of the flower becomes elon- 

 gated to 1^/2 times its diameter and its surface becomes very irregular. 

 Below each leaf and its associated bud the surface of the wall of the ovary- 

 pro trudes to form a prominent tubercle or mammilla (figs. 14, 16, 20). This 

 tubercle is at first finger-like ; later it projects farthest at its upper end and 



