2i8 THE BIOLOGY OF FLOWERING PLANTS 



the decaying organic matter of which they depend for a 

 supply of carbon compounds. All saprophytes are also 

 members of the next group. 



3. Mycoirophic plants — living in symbiosis with fungi. 

 The significance of this inter-relation for the higher 

 partner is often obscure ; in certain cases it is certainly to 

 be found in the supply of nitrogenous compounds. 



4. Plants symbiotic with bacteria — these usually benefit 

 by an enhanced supply of nitrogenous compounds. 



5. Insectivorous plants — these utilise animal food. 



§ I. Parasites 



Systematic. — Regarding parasitic flowering plants from 

 the systematic standpoint, we find that they belong to a 

 very few families {a) The Loranthaceas, the mistletoe 

 family, includes about 21 genera and 850 species ; only 2 

 genera with 5 species live as independent plants, the 

 remainder are shrubby parasites on the branches of trees 

 and shrubs. {b) The Santalaceae, sandalwood family, 

 includes about 250 species, most of which are parasitic on 

 the roots of other plants, {c) The Myzodendraceas, a small 

 family with a single genus and about a dozen species parasitic 

 on the branches of ChiHan beeches (Nothofagus). {d) The 

 Balanophoraceae, with 14 genera and about 40 species, are 

 all fleshy parasites on roots, [e] The Raffiesiaceae, with 

 7 genera and about 24 species, and (/) the Hydnoraceae, 

 with 2 genera and about 8 species, are all parasites on roots 

 or stems, {g) The score of species of Cassytha are all 

 twining parasites on the leaves and branches of tropical 

 plants. Cassytha is an isolated parasitic genus of the 

 Lauraceae, bay-laurel family, which otherwise consists of 

 independent plants, {h) The Orobanchaceas, broom-rape 

 family, has 8 genera and about 120 species, all of which 

 are root parasites, [i) Of the tribe Rhinanthoideae of the 

 Scrophulariaceas, foxglove family, about 11 genera with 

 some 350 species are root parasites, (y) The Lennoaceas is 

 a small family of sub-tropical North America with 3 genera, 



