630 



BOTANY 



PART II 



Herbs, .shrubs or trees, usually with dorsi ventral flowers with only five stamens. 

 Ovary unilocular with a simple style. There are a number of species of Viola in 

 Britain. The flowers have the anterior petal prolonged backwards as a spur, into 

 which two neetar-secreting processes of the two anterior stamens project (Figs. 686, 

 687). Many kinds of Violet have, in addition to these conspicuous flowers adapted 

 to insect pollination, inconspicuous, cleistogamous flowers which are self-fertilised 

 (cf. p. 309). J r ioia tricolor, the Wild Pansy, has large pinnately-divided stipules 

 hardly smaller than the leaf-blade itself. 



Order 19. Passiflorinae 



Flowers radial, perigynous or epigynous. Ovary of three carols, unilocular, 

 with parietal placentation ; usually three bifid stigmas. 



Family Paasifloraceae. Plants 

 climbing by means of tendrils. 

 Flowers large, complicated by out- 

 growths from the floral axis (corona 

 and disc). Passiflora, Passion 

 Flowers ; ornamental plants from 

 South America. 



Family Caricaceae. (,'"//<" 

 papaya, the Pa paw, has in its 

 latex a ferment (pa]>ayotin) re- 

 seinbling pejisin. Tropical. 



Family Begoniaceae. Herl 

 with obliquely cordate leaves. 

 Flowers unisexual. Ovary inferior. 

 Mostly tropical. Many spei-ie> of 

 Begonia are in cultivation. 



Order 20. Opuntinae ( 34 ) 



Family Cactaceae. For the 

 most part leafless plants with suc- 

 culent stems, natives of America. In 

 size they range from very small to 

 gigantic forms. Flowers hermaphro- 

 dite, actinomorphic, less commonly 

 dorsiventral. Perianth of mam 

 Two of the rib* or member8j sl ,i ra u y arranged and 



showing a gradual transition from 

 the calyx to the corolla. 8tamen> 

 and carpels numerous. Ovarv inferior, unilocular, with numerous parietal 

 placentas. Ovules with long stalks. Fruit, a berry, the succulent tissue being 

 largely derived from the stalks of the seeds. 



Peireskia and some species of Opuntia possess leaves. Other species of Ojntiitin 

 have flattened branches. Cereits, Echinocactus, with longitudinal ridges on the 

 stem ; Mamillaria has free projections (mamillre). The numerous groups of spines 

 on the shoots, ribs, or separate mamillae correspond to axillary shoots, the sub- 

 tending leaves of which are reduced while the leaves of the expanded axis of the 

 axillary shoot are metamorphosed into spines (Fig. 688). 



Fio. 688. Cereus gemnetrizans. 



ridges of a five-ribbed stem bearing flowers and fruits 

 (| nat. size). 



