104 PLANT PHYSIOLOGY AND ECOLOGY 



126. Nutrition of hysterophytes. Plants that possess chlo- 

 rophyll are holophytes, those that lack it, hysterophytes. From the 

 standpoint of nutrition, plants that make their own food by 

 photosynthesis are autotrophic, i.e., self-nourished, while colorless 

 plants are heterotrophic, i.e., nourished by material traceable more 

 or less directly to green plants. A few flowering plants are mixo- 

 trophic, i.e., while they absorb most of their food in organic form, 

 they are still able to make more or less sugar by photosynthesis. 

 Some of these, such as the mistletoe, seem to show normal photo- 

 synthesis, the parasite taking nothing but water and inorganic 

 salts from the host-plant. Others, such as the dodder, are green 

 only until they become attached to the host-plant, after which 

 the chlorophyll disappears. Hysterophytes are usually grouped 

 as parasites and saprophytes, although a large number of fungi 

 may be parasitic or saprophytic, either by choice or by neces- 

 sity. Many parasites are able to grow on a number of differ- 

 ent host-plants, and certain of the saprophytic molds can flourish 

 on almost every organic substratum. Other parasites, on the 

 contrary, are confined to a single host, and occasional sapro- 

 phytes are similarly limited in habit. 



A hysterophyte is nourished in practically the same way as 

 the embryo which receives its food from the endosperm, or as 

 the colorless tissues of a green plant, which are supplied with 

 nutriment by the chloroplasts. The deep-seated cells of a wheat 

 stem depend upon the leaves for food just as the rust upon it 

 does, and the processes of digestion and of respiration are essen- 

 tially the same in both. The saprophyte, though less directly, is 

 similarly dependent upon the activity of green leaves for the sugar, 

 starch, cellulose, oil, or proteid which it digests and absorbs. The 

 respiration of many saprophytes is likewise similar to that of root- 

 cells and of parasites, but in a large number, especially )'easts, 

 molds, and bacteria, respiration implies fermentation. For this 

 reason, saprophytes often grow readily in solutions containing 

 organic acids, which are the products of fermentation. 



127. Kinds of parasites. The type of parasitism in which the 

 presence of the parasite benefits the host-plant in some measure 

 is commonly distinguished as symbiosis or mutualism. Such a 

 relation is found between certain fungi and the roots of many 

 trees, the beech, oak, pine, spruce, etc., in Monotropa, and in the 

 root-like stems of the coral-root, Corallorrhiza. The root with 



