THE NUTRITION OF PLANTS 157 



119. Saprophytes. — In the case of saprophytes dead bodies 

 or body products are attacked, and sooner or later all or- 

 ganic matter is attacked and decomposed by them. The de- 

 composition is a result of the nutritive processes of plants 

 without chlorophyll, and were it not for them " the whole sur- 

 face of the earth would be covered with a thick deposit of 

 the animal and plant remains of the past thousands of years." 



The green plants, therefore, are the manufacturers of or- 

 ganic material, producing far more than they can use, while 

 the plants without chlorophyll are the destroyers of organic 

 material. The chief destroyers are the Bacteria and ordi- 

 nary Fungi, but some of the higher plants have also adopt- 

 ed this method of obtaining food. Many ordinary green 

 plants have the saprophytic habit of absorbing organic ma- 

 terial from rich humus soil ; and such plants as the broom 

 rapes are parasitic, attaching their subterranean parts to 

 those of other plants, becoming " root parasites." 



120. Parasites. — Certain plants without chlorophyll are 

 not content to obtain organic material from dead bodies, 

 but attack living ones. As in the case of saprophytes, the 

 vast majority of plants which have formed this habit are 

 Bacteria and ordinary Fungi. Parasites are not only modi- 

 fied in structure in consequence of the absence of chloro- 

 phyll, but they have developed means of penetrating their 

 hosts. Many of them have also cultivated a very selective 

 habit, restricting themselves to certain plants or animals, 

 or even to certain organs. 



The parasitic habit has also been developed by some of 

 the higher plants, sometimes completely, sometimes par- 

 tially. Dodder, for example, is completely parasitic at 

 maturity (Fig. 148), while mistletoe is only partially so, 

 doing chlorophyll work and also absorbing from the tree 

 into which it has sent its haustoria. 



That saprophytism and parasitism are both habits grad- 

 ually acquired is inferred from the number of green plants 

 which have developed them more or less, as a supplement to 



