454 ANGIOSPERMAE—DICOTYLEDONES 



pollen-covered lobes towards the interior of the flower. There is next a second 

 rotation of 90° into a horizontal plane cutting the first at right angles, so that 

 the anther finally comes to be at right angles to the tip of its filament with its 

 dehisced surface facing downwards. The three purple-flecked styles with iheir 

 green capitate stigmas curve upwards, and project about 10 mm. beyond the anthers. 

 Autogamy would seem to be excluded under such circumstances, )'et it is possible 

 that the stigmas and anthers may be brought into contact when the flower closes 

 at the end of the single day's anthesis. This is the more probable as Warnstorl' 

 saw a fully formed fruit in a greenhouse. Here then, there is apparently a case 

 in which an obviously chasmogamous flower is only self-pollinated after it has 

 closed. The pollen-grains are golden-yellow in colour, adhesive, conico-tetrahedral, 

 with low anastomosing ridges or folds, 63-75 /j. in diameter. 



Visitors. — Delpino has observed humble-bees and the carpenter bee Xyloco]).!. 

 violacea (' Sugli appar. d. fecondaz. nelle piante autocarp.,' p. 31 ; Hildebrand, Ijoi. 

 Ztg., Leipzig, .xxv, 1867, p. 284). 



1077. P. princeps Lodd. { = P. racemosa Brot). — According to Delpino (' I'll. 

 OSS.,' pp. 170, 172), the corolla-tube is divided into three chambers by circlets ol 

 rays, the lowest containing the nectar, which only discriminating visitors can reach. 



Visitors. — Delpino supposes these to be humming-birds. Fritz Miiller (Henii. 

 Muller, 'Fertilisation,' p. 268) actually observed them in Brazil on flowers of 

 species of Passiflora. He is of opinion that the latticed work in the upper part 

 of the corolla-tube is not for the purpose of keeping out unbidden guests, but for 

 trapping small insects to serve as food for the humming-birds, in return for which 

 the latter effect pollination. 



311. Papaya Tourn. 



1078. P. carica L. ( = Carica Papaya L.). — According to Baillon (Bull. soc. 

 linn., Paris, i, 1887), the species is usually dioecious, but often monoecious under 

 cultivation. A plant reared in a greenhouse from Bourbon seed produced flowers 

 which were all male. When transplanted to the open air, the terminal flowers of 

 numerous inflorescences were female, and after these were fertilized the originally 

 male plant set a number of good rapidly growing fruits. 



XLVl. ORDER CUCURBITACEAE JUSS. 



Literature. — Knuth, ' Grundriss d. Blutenbiol.,' p. 55. 



Species monoecious, or more frequently dioecious. The male flowers are largei- 

 than the female ones, so that insects usually pay their first visits to the former. 

 The nectar is secreted in the bottom of a naked fleshy cup formed by the fusion 

 of the lower parts of calyx and corolla. On the stamens of many species there 

 are numerous glands, which, when their tips are broken off, serve to moisten the 

 pollen-grains and make them sticky, according to Halsted. 



Arcangeli (Atti del congresso bot. internaz., 1892, pp. 441-54, Geneva, 189-j) 

 describes the flower mechanism, and especially the nectaries of various Cucurbitaceac. 

 i. e. Cucurbita maxima Duch., C. Pepo E., Lagenaria vulgaris Se'r., Cucumis Melo Z., 

 Benincasa, Ecballion, ;\Iomordica, and Trichosanthes. Bees are particularly active 



