I3O GROWTH AND WORK OF PLANTS 



formation of excrescences or galls, as in corn smut, the cedar 

 apples, azalea apples, black knot of the plum and cherry, leaf 

 curl of peach, plum pockets of the plum, etc. 



NUTRITION OF SAPROPHYTES. 



313. Humus saprophytes. Humus is composed of organic 

 matter, largely plant remains in a state of decay. It is abundant 

 on the forest floor and in moors where the decomposition of the 

 plant remains is slow and incomplete. As stated in the opening 

 paragraph of this chapter, saprophytes are plants which grow and 

 feed on dead or decaying organic matter. Humus saprophytes 

 are those plants which grow in and feed on humus. The humus 

 is not easily soluble, and is rendered available as food for the higher 

 plants by the solvent action of fungi and bacteria. Many fungi, 

 especially the mushrooms, toadstools, puff balls, etc., are humus 

 saprophytes. Many species grow in the forest. The threads of 

 mycelium permeate through the humus carrying on the disinte- 

 gration which was begun by other species and by bacteria, and 

 appropriating for food some of the dissolved substances. It is by 

 this means that the fungus part of the mycorhiza (see paragraph 

 205) prepares food for the forest trees with which it is associated. 

 Some of the flowering plants which grow in humus lack chloro- 

 phyll, and some or all of their roots are mycorhizae. These are 

 also regarded as humus saprophytes. The Indian pipe (Mono- 

 tropa) is one of these. This is a pretty little plant usually growing 

 in a cluster 15 to 20 cm. (6-8 inches) high. It is white in color, 

 sometimes with a reddish tinge. The stems are straight and 

 fleshy, the leaves are scale-like and lack chlorophyll. The flower 

 in one common species (M. uniflora) is single, and is turned on 

 the stem like the bowl of a pipe. This plant obtains its food 

 through the mycorhiza. This mycelium has the power of dis- 

 solving some of the carbohydrates in the humus and passing it 

 over to the mycorhiza so that the plant can be supplied in this way 

 with the carbohydrate food which it cannot make from the carbon 

 dioxide of the air because of the absence of chlorophyll. 



