1842 



A TEXTBOOK OF THEORETICAL BOTANY 



mention Mabea, Manihot and Saphim, but in none is the yield so large or 

 the rubber as good as that obtained from Hevea brasiliensis. 



Fig. 1744. — Hevea brasiliensis. Rubber plantation in Ceylon. Photograph supplied by 



courtesy of the Imperial Institute. 



The genus Jatropha deserves mention. There are about 200 tropical 

 and subtropical species. J. podagrica is a xerophyte with a swollen stem 

 which consists mainly of water-storage tissue. Other species are widely 

 cultivated as ornamental plants while J. ciiras is the Physic nut. Aleurites 

 moluccana and Sapium sebiferiim yield oils and fats. 



Another genus of great importance is Manihot (Fig. 174s)- There are 

 about 150 species, occurring from Mexico to South America. They are 

 either shrubs or herbs. M. palmata is the Sweet Cassava or Mandioc and 

 M. utilissima (Fig. 1746) is the Bitter Cassava. Both are extensively culti- 

 vated in the tropics on account of the valuable starchy food (arrowroot and 

 tapioca) obtained from the large tuberous roots. We shall refer to their 

 preparation in Volume IV. 



M. glaziovii provides the Ceara rubber of commerce which is obtained 

 by tapping in a manner similar to that employed for Para rubber. 



Codiaeiim variegatiitn is the source of the " Crotons " so often cultivated 

 in greenhouses on account of their magnificent foliage. Other species are 

 employed for making hedges in the tropics. 



From the above rather long account of the family it will be seen that not 

 only is it represented by many large genera, but that many and varied are 

 the uses made of them by man. The chief centre of geographical distribu- 



