. British plants : their biology and ecology. Plants; Plant ecology. 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, whi
. British plants : their biology and ecology. Plants; Plant ecology. 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—, pine—and with plants living in peat—, 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 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. harmless, or even. Please note tha
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