EOOTS 35 



HerliaceoUN perennials, like the dahlia (Fig. 23 J and the 

 common rhubarb, store food in the root during the summer, 

 and consume part or all of it in the growth of the following 

 spring. Trees and shrubs in temperate or cold climates store 

 starch and other foods in the roots, as well as the stem, dur- 

 ing the winter. It is the stored food in the root that enables 

 such plants as rhubarb, the peony, some buttercups, sweet 

 cicely, the dandelion, and many others to make a quick growth 

 in the spring before the weather is warm enough for the man- 

 ufacture of much plant food. The starch, sugar, and proteins 

 ■nhicli abound in many roots or root-like portions of plants 

 make them valuable for food, as in the case of beets, turnips, 

 carrots, parsnips, sweet potatoes, salsify, and in the cassava 

 plant, from which tapioca is made. 



It is frequently the case that desert plants store large 

 quantities of water in their roots or in combinations of roots 

 and underground stems, and are thus able to survive long 

 periods without rain. 



35. Roots in relation to other organisms. The roots of the 

 higher plants often enter into complicated relations with plants 

 of other species or with animals. Before discussing these re- 

 lations it is necessary to state briefly what some of them are. 

 A plant or animal Avhich feeds in whole or in part on the sub- 

 stance of another living organism is called a pnnisite. Familiar 

 examples of animals parasitic on other animals are fleas and 

 ticks. The organism which supports a parasite is called the 

 Jioif. Organisms which live together in a mutually helpful 

 way are said to be mutualists or sometimes are called mess- 

 mates. Roots may be : 



(1) Parasitic on other roots or stems. 



(2) Hosts for parasitic roots. 



(3) Hosts for parasitic animals. 



(4) Messmates or mutualists with other organisms. 



36. Parasitic roots. A good many of the higher plants feed 

 altogether or partially on the sap which they draw from other 

 living plants. Those which live entirely at the expense of the 



