380 General Botany 



can even synthesize their own carbohydrates. An animal can 

 transform carbohydrates into fat, but it apparently lacks the 

 power to make certain vitamins and several of the amino acids 

 needed in protein synthesis. 



Parasites. An organism that derives its food directly from 

 another living organism is called a parasite. A parasitic plant 

 may live inside the host, from which it secures food, as is the case 

 with many bacteria and fungi. Or a parasitic plant may be 

 merely attached to the host plant at one or more points. Beech 

 drops are small, purple, flowering plants attached to the roots 

 of beech trees. The dodder, or " gold thread," is a slender, 

 yellow, climbing plant, related to the morning-glory, that becomes 

 attached to the stems of a great variety of hosts by means of 

 small, root-like structures {haustoria; singular, haustorium) that 

 penetrate the cortex of the host and finally reach the conductive 

 tissues (Fig. 239). 



True parasites among the flowering plants are generally small ; 

 their leaves are mere scales, and the most prominent parts are the 

 flowers and the reproductive structures. In color they vary 

 from yellow to red and purple. Some apparently do not injure 

 the host plant ; others may injure and eventually kill the plant 

 on which they grow. 



Partial parasites. Some parasites contain chlorophyll and 

 are able to manufacture at least a part of their foods. For 

 example, the mistletoes occur on a great variety of trees from the 

 Atlantic to the Pacific, and are very common particularly in the 

 subtropics. The sticky seeds adhere to the bark of branches, 

 and a root-like haustorium dissolves its way into the bark and 

 forms a connection with the conductive tissues of the host 

 trees. Mistletoes sometimes form much-branched masses of 

 stems and foliage 2 or 3 feet in diameter. These plants have 

 lost the power of growing on soils, and apparently are dependent 

 on their hosts for their water supply and a part of their foods. 

 They may be called partial parasites. 



