THE FRUIT OF OPUNTIA FTJLGIDA. 57 



EXPLANATION OF PLATES. 



ABBREVIATIONS USED IN PLATES. 



a., areole or cushion formed by axillary bud; a. I., abscission layer; 6., bristle or 

 glochidium; 66., barb of bristle or of spine; c, carpel; cfc., cork; cm., cambium; 

 c. c, crystal containing cell; c. t., conducting tissue of style; c. w., cell-wall; e., epi- 

 dermis; em., embryo; ep., endosperm; /., flower; fu., funiculus or stalk of ovule; 

 g. c, guard-cell; g. p., growing-point; h., hypodermis; i., integument; I., leaf; Z. s., leaf- 

 scar; n., nectary; o., ovary; ov., ovule; p., petal; pft., phellogen; pi., palisade; p. s., 

 perianth-scar; r., root; s., sepal; sa., stamen; s. c, slime-cell; sd., seed; sg., stigma; 

 sTi., sheath of spine; so., stoma; sp., spine; st., stem; sy., style; t., trichome; tt., 

 tubercle; v. 6., vascular bundle; to. f. wall of fruit. 



Feontispibce. 

 Photograph of a mature plant of Opuntia fulgida on reservation of Desert Laboratory 

 at Tucson, showing a frequent type of forked trunk, due to injury of main 

 axis, also the branching habit and clusters of fruit. The nesting bird is the 

 cactus wren, Heleodytes hrunneieapillus ccmesi (Sharpe). [D. T. MacDougal 

 photo.] 



Plate 1. Photogeaphs of Opunha FuiGmA. 



Fig. 1. A fruiting plant growing in the desert at Tucson. Photographed April 25, 

 1915. X 0.03. 



Pig. 2. Heavily fruiting branches of a tree on the campus of the University of Arizona. 

 The largest cluster included more than 100 fruits. Photographed in 

 May 1912. X 0.1. 



Fig. 3. A single large cluster of fruits from the same tree as figure 2. X 0.3. 



Fig. 4. A vegetative joint and fruits of 1914 bearing buds of flowers of 1915. Photo- 

 graphed in May 1915. X 0.6. 



Plate 2. Photogeaphs of O. FULaiDA. 



Fig. 5. Tip of a vegetative joint with young joints still bearing the evanescent leaves, 

 showing also areoles with spines and nectaries. X 0.9. 



Fig. 6. Four generations of flowers and fruits developed from a vegetative joint in the 

 season of 1915. This cluster, collected at Tucson and photographed in 

 mid-July 1915, shows the relative sizes of the four generations. No. I 

 opened in May; II in June; III, if not removed from the plant, would 

 have opened in late July; IV in late August. Note that some members 

 of generation III (at right below) have but barely pushed out of the 

 areole. X 0.6. 



Fig. 7 a, 6, c. Joint-fruits and pseudo-fruits, showing several structures combining in 

 various degrees the characters of vegetative joint and fruit. X 0.45. 



F^G. 8. Cluster of 11 secondary fruits borne on a single primary fruit showing the 

 persistence of fruits over one, two, or more winters. Photographed 

 April 1915. X 1. 



Fig. 9a. Joint of 1914 bearing opened and withered flower of 1915, the latter with 

 buds of secondary flowers on its sides. X 0.6. 



Fig. 96. Similar joint bearing primary flowers. In the areoles of these are borne 

 trichomes, nectaries, and buds of secondary flowers. Many of the latter 

 bear numbers of the awl-shaped deciduous leaves. X 0.6. 



Plate 3. Drawings of O. fulgida. 



Fig. 10. Radial section of an axillary bud of flower, showing growing-point, nectary, 



spine, etc. X 25. 

 Fig. 11. Longitudinal section of a flower bud through a placenta, mammillae, leaves, 



two axillary buds, a nectary, etc. X 3.33. 



