THE FOOD OF PLANTS 35 



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

 surface 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 

 organic 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 ordinary Fungi, but some of the higher plants have 

 also adopted this method of obtaining food. Many ordinary 

 green plants have the saprophytic habit of absorbing organic 

 material from rich humus soil ; and some plants (as broom 

 rapes) are parasitic, attaching their subterranean parts to 

 those of other plants, becoming what are called " root para- 

 sites." In cases of mycorhiza (see p. 87), which are now 

 thought to include great numbers of green plants, it is sup- 

 posed that some organic material is brought in by the fungus. 



57. 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. 75), 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 

 24 



