38 



PRACTICAL BOTANY 



38. Partnership of roots and filaments of fungi. Many of the 

 flowerless plants known by the general name of fungi form 

 a dense network of very minute threads. Such a network is 

 found in intimate association with the roots of many kinds of 

 flowering plants. It is especially com- 

 mon on the roots of those which cannot 

 manufacture plant food by photosyn- 

 thesis, but it also occurs on other plants 

 with green leaves, such as pines and 

 beeches. On the roots of the beech 

 the fungus filaments are found united 

 into a sort of membrane, covering the 

 tips of the young roots and extend- 

 ing back for a considerable distance 

 (Fig. 24). In such plants as the heaths, 

 blueberries, and their relatives, the 

 fungus threads form little tangled 

 masses inside the cells near the sur- 

 face of the root and send out free ends 

 into the surrounding soil. In any case 

 the whole filamentous mass living in 

 connection with the root is called a 

 mycorrhiza. Roots provided with my- 

 corrhiza usually form few or no root hairs, and it is supposed 

 that the fungus threads to some extent perform the work of 

 root hairs in absorbing soil water. The subject is not yet 

 well understood, but it would seem that certain trees, such as 

 pines and oaks, do not flourish as well when grown in a soil 

 which does not develop a mycorrhiza upon their roots. 1 



i See "Experiments in Blueberry Culture," Bulletin 193, Bureau of Plant 

 Industry, U.S. Dept. Agr. 



FIG. 24. Tip of a root of 



European beech, covered 



with mycorrhiza 



The coating has been stripped 

 off for a little way at the 

 top to show the thickness of 

 the mycorrhiza. Magnified 

 30 diameters. After Pfeffer 



