54 THE FRUIT OF OPUNTIA FULGIDA. 



of the vascular bundle may participate in the formation of the cells of the 

 abscission layer. The cells of the vascular bundle in line with the abscission 

 layer seem to degenerate and rupture as a result of the split in the adjoining 

 tissues. The whole funnel-like scar left at the top of the ovary by the fall of 

 the perianth is soon protected by several layers of periderm. These arise 

 from a phellogen formed but a few layers within the abscission layer. One, 

 or sometimes several, layers of this periderm may have the cell-walls greatly 

 thickened to form a schlerenchymatous protective layer. 



From the axillary buds, or areoles, of the primary flowers that open in 

 May, arise secondary flowers which open in June. From areoles of these, in 

 turn, tertiary flowers open in July, and on the latter quaternary flowers 

 bloom forth in August. Thus four and sometimes five generations of flowers 

 may be formed each season. Often two or three and sometimes four genera- 

 tions of persistent fruits may thus arise in a single summer. 



The number of well-matured seeds occurring in a fruit may range from 

 to 100 or even 200. Large numbers of sterile seed-rudiments of various 

 sizes are found in most fruits, some of them evidently having degenerated 

 soon after their initiation. The fertile seed contains a large coiled embryo 

 and a small mass of endosperm in the loop between radicle and cotyledons. 

 The seeds of this opuntia have not, so far as is recorded, been Icnown to ger- 

 minate in the field under natural conditions. They were germinated in the 

 laboratory by slightly chipping the seed-coat. The seeds may remain 

 unchanged and capable of germination for several or many years while 

 embedded in the pulp of the persistent, attached fruits, or even in that of 

 fallen, rooted ones. The seeds are set free in nature only by the decay of 

 the pulp of the fallen fruit, or when the fruits are eaten by browsing animals. 

 It is possible that the failure of the seeds to germinate in the moist pulp of 

 the fruit, even during the hot summer, may be due to the impenetrability of 

 the seed-coat. Even chipped seeds, however, do not germinate in this 

 medium as they do in soil or on wet filter-paper, which suggests that the pulp 

 may have an inhibitory effect on some process connected with germination. 



The mature fruit, unripened, remains attached to the tree after the ripen- 

 ing of the seeds. It may thus persist and grow year after year, by the aid 

 of a cambium ring. It is this persistent fruit that gives rise to flowers, just 

 as a stem would. By the proliferation of the primary flowers, so formed, 

 secondary and tertiary flowers arise and develop to persistent fruits, two, 

 three, or even four generations per season. In the course of several years a 

 cluster may arise containing scores of fruits with sometimes 10, 12, or even 

 14 generations of fruits in a continuous linear series. 



Only in two cases, among hundreds examined, were attached fruits found 

 proliferating to vegetative joints. 



Fallen fruits that rest on moist ground may give rise to adventitious roots, 

 from areoles, perianth-scar, or stalk-scar, and then to vegetative shoots, from 

 areoles only, and thus initiate new individual plants. In nature this origin 



