THE DICOTYLEDONES 



1839 



used medicinally. Other large genera included are Antidesma, with 150 

 palaeotropical species, and Baccaiirea with sixty species occurring in Africa, 

 Asia and Polynesia. 



In the Crotonoideae, the single genus Croton is important. It is a large 

 tropical genus containing about 600 species. A pentamerous calyx and 

 corolla are present though the latter may be absent from the female flowers. 

 The stamens are very numerous, some species having as many as a hundred. 

 The females normally have three carpels. 



C. tiglhim, found in Asia, is the source of Croton Oil which is expressed 

 from the seeds. It is used as a powerful purgative drug. C. cascarilla and 



./ 



Fig. 1741. — Mercurialis perennis. Left, flowers on female plant. Right, male plant. 



C. eleuthera are the source of Cascarilla Bark which is used as a tonic. They 

 are cultivated in the West Indies. C. lacciferus, which grows in India and 

 Ceylon, yields a lac which is used in high-class varnishes. Several of the 

 Brazilian species provide Dragon's Blood resin. In the large tribe Acaly- 

 pheae are a number of important genera. It includes the two British 

 genera Euphorbia and Mercurialis (Fig. 1741) and also many tropical genera. 

 Euphorbia itself is a genus of some 750 species. Though the British species 

 show a considerable family resemblance to one another, the same can 

 scarcely be said of those from warmer climates. Many of them live under 

 dry conditions and are succulent in character and devoid of leaves. Under 

 such conditions therefore they resemble very closely some of the Cacti. 

 Many are armed with thorns, and in general it is the stem which becomes 

 fleshy. Laticiferous tissue is present and the succulent Euphorbia splendens 

 (Fig. 1742) is often used botanically to illustrate this structure on account 

 of the thick-walled tubes with dumb-bell shaped starch grains which it 



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