626 



BOTANY 



PART II 



and each male flower are provided with a small perianth. The whole cyathium, 

 which is an inflorescence, is always enclosed by five involucral bracts ; alternating 



with these are four nectar-secreting glands, 

 the presence of which increases the likeness 

 between the cyathium and a flower. The fifth 

 gland is wanting, and the inverted female flower 

 hangs down in the gap thus left. Between the 

 groups of male flowers which stand opposite 

 to the bracts (Fig. 624) are branched hairs 

 which are visible when the cyathium is cut 

 through longitudinally (Fig. 623 B). The 

 cyathia are usually grouped in dichasia, and 

 these in turn form an umbellate inflorescence, 

 with three to many branches. It often 

 happens that the female flower is only de- 

 veloped in some of the cyathia, remaining 

 rudimentary in the others. Many species of 

 Euphorbia, especially the African species, are 

 succulent-stemmed plants resembling Cacti in 

 general appearance (Fig. 625). 



Euphorbia, like many but not all the other 

 plants of the family, contains a milky juice, 

 which is secreted in non-septate latex-tubes. 

 This juice, which in many cases is poisonous, 

 exudes wherever the plant is wounded. 



An important constituent of the latex of 

 species of Hevea (H. Sieberi, discolor, rigidi- 

 folia, paucifolia, lutea, guyanensis, Spruceana} 

 is CAOUTCHOUC (of. 19 ). As Para Rubber 

 obtained in the tropics of South America, 

 especially in the Amazon Region, this affords 

 about one-half of the total rubber supply. In 

 addition Manihot Glaziovii, another South 

 American plant of this order, which yields 

 Ceara Rubber, must be mentioned. A nearly 

 related plant, Manihot utilissima, provides in 

 its tuberous roots a very important food in 

 the tropics. The starch obtained from these 

 roots forms mandioc or cassava meal, the finest 

 varieties of which, as tapioca or Brazilian 

 arrowroot, are of commercial importance. 

 The shrub, which is a native of Brazil, is now 

 cultivated throughout the tropics. 



Ricinus communis (Fig. 626) is a tall shrub 

 of tropical Africa. In our climate it is annually 

 killed by the frost. The hollow stem bears 

 large palniately-divided leaves. The terminal inflorescences (Fig. 627) are over- 

 topped by vegetative lateral branches. The male flowers, situated towards the 

 base, have a membranous calyx of 4-5 sepals, enclosing the branched stamens ; 

 the end of each branch bears a theca. The female flowers, nearer the summit of 

 the inflorescence, have 3-5 sepals and a large tripartite ovary. The latter is 



FIG. 627. Ricinus communis. Inflor- 

 escence (i nat. size) ; young fruit cut 

 through longitudinally. OFFICIAL. 



