130 GENERAL BOTANY 



This porous spongy layer, readily absorbs any water, 

 that, like rain, may fall on it, and also allows air 

 to reach the green layer underneath, and thus these 

 roots act both as true roots in absorbing moisture, 

 and also like leaves in assimilating carbon from the 

 air. It seems very likely too, that nitrogen in the 

 form of ammonia, produced by the decay of vege- 

 table and animal matter, may be absorbed in the 

 damp spongy tissue and ultimately made use of by 

 the plant. 



5. All the types we have been considering have 

 been normal green plants, absorbing their food-ma- 

 terials from soil and air by their own roots and 

 leaves. There are, however, plants which depend 

 wholly or in part on others for their water and food. 

 These are called parasites or semi-parasites, as the 

 case may be, and the plants they feed on are called 

 their hosts. 



SXRIGA is a very common semi-parasite on the 

 plains, growing on the roots of SORGHUM and other 

 grasses, to which it attaches itself by little round 

 tubercles, called haustoriums. The Sandalwood tree, 

 SANTALUM ALBUM, is another, for it attaches itself 

 to the roots of shrubs, such as LANTANA, by similar 

 haustoriums, and LORANTHUS is a very common 

 semi-parasite on the branches of trees, into which 

 it sends special sucking organs to draw the sap. 

 These semi-parasites have all chlorophyl in their 

 leaves, and are, therefore, able to assimilate car- 

 bon and manufacture a certain amount of food- 

 materials for themselves, but they seldom have the 

 full green colour of a normal plant. 



