Minnesota Plant Life. 



89 



encircling the roots of many kinds of trees or herbs, and some- 

 times developing within the outer tissues of roots or under- 

 ground stems belonging to plants growing in very rich soil. 

 An example of the first kind is to be met with on rootlets of the 

 tamarack. Another is found upon the rootlets of the oak, and, 

 often, too, upon the young roots of birches. Such fungi form 

 rather thin, felted masses inclosing the roots as in sheaths. The 

 sheaths become of a dark brown color as they grow older, but 

 at first they are almost white. So constant is the association 

 of the fungi with the roots or subterranean stems of some plants 

 that they may be regarded as necessary concomitants of these 

 higher plants. It is probable that they play a very important 

 part in the nourishment of roots which they inclose or infest. 

 It would seem that they have something to do with the conver- 

 sion of the food materials in the soil into a condition in which 

 they are the more easily absorbed and assimilated by the roots 

 themselves. If this suggestion, which is generally accepted 

 among botanists, is the correct one, there is presented the inter- 

 esting fact that all the tamarack trees in a swamp and all the oak 

 trees by the road-side are largely dependent for their life and 

 prosperity upon the little sheaths of fungi which feed their roots. 

 In a considerable number of plants the fungal threads do not 

 form a sheath around the outside of the root but grow in mi- 

 croscopic tangled masses resembling skeins of yarn, one mass 

 in each of certain outside cells of the root. The orchids of Min- 

 nesota are provided with such structures in their roots and the 

 Dutchman's pipe, the Pyrolas, and a number of other plants 

 which live in humus soil, resemble the orchids in this respect. 

 Sometimes underground stems among the orchids are, through 

 the irritation of the fungus in their outside cells, peculiarly knot- 

 ted and distorted into structures quite different from the ordi- 

 nary forms of growth. A very good example of this is the 

 coral-root orchid. Really this variety of orchid has no roots at 

 all and the underground portion is a curiously modified branch- 

 ing root-stock, which from its resemblance to coral, gives occa- 

 sion for the common name of the plant. There is good reason to 

 suppose that some of such underground fungus-masses which 

 enclose the roots of trees, or develop themselves in the roots of 

 humus plants, were originally the vegetative bodies of truffle- 



