THE DICOTYLEDONES 



1813 



British example is Thesium humifusiim (Fig. 1710) (Bastard Toadflax) which 

 is a root parasite on grasses. This genus which contains about 235 species 

 has its centre of distribution in South Africa. The genus Santahim, with 

 ten Indo-Malayan and Polynesian species, consists of large, parasitic trees. 



Fig. 1710. — Thesium liiimifiisum. Habit of plant. 



S. alburn is the source of the fragrant Sandalwood, which is used in cabinet- 

 making. A perfumed oil may be distilled from it. The fruits of several 

 species possess edible, sweet pericarps. Species of Exocarpus are valuable 

 for their timber, while the hard nuts are borne on fleshy, edible stalks and 

 are called Australian Cherries. 



It is convenient here to refer to another small order, the Rhamnales, 

 They show a marked similarity to the Celastrales but the tendency to form 

 unisexual flowers is more pronounced and they are sometimes apetalous. 

 The gynoecium usually consists of five carpels, more rarely two, which are 

 united to form a chambered ovary, each loculus of which contains two 

 anatropous, ascending ovules. The plants are either shrubs or trees with a 

 tendency to become hanas. Two families are included, the Rhamnaceae 

 and the Vitaceae. 



The Rhamnaceae contain about forty genera and 500 species which 

 are very widely distributed. Rhammis contains 100 species of which two 

 are wild in Britain. R. catharticus (Buckthorn) which grows chiefly on 

 the chalk in southern England and R. frangula which is widely distributed 

 in England although rare in Scotland. Its centre of distribution is central 

 Europe. Another genus, Zizyp/iiis, with forty species, occurs in Indo- 

 Malaya. The plants are stipulate, the stipules being developed as thorns, 

 one of which turns upwards and the other downwards. Sometimes only 

 one develops. Z. vulgaris and Z. lotus have edible fruits, the former being 

 known as the French Jujube (Fig. 171 1). The latter was the food of the 

 legendary Lotus eaters. Z. chloroxylon of Jamaica provides a hard, tough 

 timber known as Cogwood. 



