SAPROPHYTES 



125 



mycorhiza, associated with their roots. The saprophyte 

 at first made use of it merely to obtain water, but in the 

 course of time it increased its demands, and at last came 

 to rely upon it for all its food. Since light is unnecessary, 

 saprophytes can escape competition by living in the 

 densest shade of forests, where a green plant could not exist. 



(ii.) Partial Saprophytes. Many 

 green plants also possess a mycor- 

 hiza, and indirectly, therefore, live 

 on humus. This is the case with 

 many of our forest-trees, which in- 

 habit a soil rich in a somewhat acid 

 humus e.g., pine and with plants 

 living in peat e.g., heath. The 

 mycorhiza is at first external on 

 the roots and functions merely as 

 root-hairs, but in those cases where 

 it penetrates deeply in the tissues, 

 its value to its partner increases, 

 and it passes on to it something 

 more than water ; in fact, condi- 

 tions are being established which, 

 in the course of time, may lead to 

 the degeneration of the green plant 

 into a colourless saprophyte. 



(b) Parasites (Gr. parasites, one 

 who sups at another's table). 

 These obtain the materials for their 

 nutrition carbohydrate and pro- 

 tein from living hosts, animals or 

 plants. Among the lower plants 

 many fungi are parasitic, and some 

 that are saprophytic are capable 

 of becoming so, if circumstances 

 allow. Swarms of bacteria are 

 parasites, and though some are harmless, or even 

 beneficent, others are malignant and give rise to disease. 

 These lower plants are usually internal parasites, in- 

 habiting the tissues of animals or plants. Higher 

 plants which are parasitic attach themselves extern- 

 ally to the bodies of other plants, and by means of 

 special sucking organs haustoria penetrating the 

 tissues, absorb nutriment from them. The depend- 



FIG. 40. Corallorhiza 

 innata (CORAL - ROOT 

 ORCHID). 



Note the scale -like leaves, 

 underground stem, and 

 absence of roots. 



