THE FRUIT OF OPUNTIA FULGIDA. 59 



FiQ. 33. Transverse section of the sterile base of the same flower bud as that shown 



in figure 29, showing the ring of vascular bundles, with fascicular 



cambium already established. X 5. 

 Fig. 34. Transverse section of an older flower bud through seven styles or stigmas, 



the stamens, petals, and sepals. X 5. 

 Fig. 35. Part of an approximately transverse section of the flower shown in figure 34, 



giving details of structure of style and stigma, including the papillose 



lining of the stylar canal. X 20. 



Plate 5. 



Fig. 36. Part of transverse section of a stigma, showing papillose surface, and the 

 conducting tissue, vascular bundle, slime-cells, etc., within. X 75. 



Fig. 37. Transverse section through the flower shown in figure 34, showing style, 

 stamens, and wall of ovary with its tubercles, areoles, etc. X 3. 



Fig. 38. Part of transverse section of young ovary, showing long-stalked ovules with 

 integuments initiated, and archesporial cell differentiated. X 24. 



Fig. 39. Transverse section of a young ovary, showing seven placentas with numerous 

 anatropous ovules, also the vascular structure and radial arrangement 

 of photosynthetic cells in tubercle. X 4. 



Fig. 40. Transverse section of slightly older ovary, showing the filling up of the 

 ovarian cavity by the growth of the young ovules and their stalks. Note 

 that the magnification is but half that of figure 39. X 2. 



Fig. 41. Transverse section of mature ovary showing two nearly ripe seeds and a 

 larger number of sterile seeds that have ceased growing at various 

 stages of development. X 2. 



Fig. 42. Transverse section of a persistent, fertile fruit several years old, showing 

 seeds and their stalks completely filling ovarian cavity, the great radial 

 growth of the vascular bundles, and the loss of prominence of the 

 tubercles. X 2. 



Fig. 43. Transverse section of the sterile base of a fruit like that of figure 42, show- 

 ing the large central mass of water-filled parenchyma, the radial growth 

 of the vascular bundles from the activity of the fascicular cambium, and 

 the generally smooth, rounded outline of the surface. X 2. 



Fig. 44. Transverse sections of vascular bundles from ovaries of various ages, all at 

 same magnification, to show relative growth of the phloem and xylem 

 regions of the bundle, (a) From ovary of a fiower from which the 

 perianth has just fallen; (b) from one-year fruit; (c) from a fruit 6 or 

 8 years old, 35 millimeters in diameter. X 11. 



Fig. 45. Transverse section of lower third of nearly mature leaf from the ovary of a 

 flower about ready to open, showing flattened form, vascular system, 

 slime-cells, and the slightly specialized palisade. X 42. 



Fig. 46. Transverse sections near tip of leaf from flower bud, showing small vascular 

 strand, slightly developed palisade, and large air-canals. X 50. 



Fig. 47. Surface view of a flower bud some time before opening, showing sepals and 

 petals and six areoles. Two of the latter have already initiated flower 

 buds, in which the spindle-shaped leaves of lower part of ovary and the 

 flattened sepals and petals can be distinguished. Each of the remaining 

 areoles shows a leaf-scar and the dense tuft of trichomes, with its inner 

 border of spicules and its one or several embedded nectaries. X 3. 



Plate 6. 



Fig. 48. Part of transverse section near top of opening flower, showing upper surface 

 of an areole and a cross-section of the subtending leaf. Among the 

 trichomes of the areole are ten nectaries, and about its inner border is a 

 group of a dozen or more bristles or glochidia. X 2. 



Fig. 49. Part of a transverse section of a recently opened primary flower, showing 

 edge of cup of flower and three tubercles, one of them bearing an areole 

 with two nectaries and the bud of a secondary flower. The arrow indi- 

 cates the sagittal plane. X 3. 



