66 BOTANICAL GAZETTE [JANUARY 
The mycorhiza of forest trees.—Some important experiments have been 
carried on by Joser Fucus’? with the mycorhiza of forest trees. The chief 
object of the experiments was the synthetic production of mycorhizas by 
bringing together pure cultures of the two symbionts. The trees employed 
were various conifers, and the fungi consisted of a number of humus-inhabiting 
forms. Most of the experiments gave negative results, but when six-month 
seedlings of Pinus Strobus were brought into contact with cultures of Collybia 
macroura, a strong development of endotrophic mycorhiza was secured. The 
finding in certain cultures of spores and mycelia quite unlike those used in the 
inoculations caused Fucus to believe that root infection often may come from 
the seeds rather than from the substratum. Picea seedlings eight days old 
growing in sterilized humus had their roots infected by fungi. The infected 
cells of the conifer roots soon turned brown and were cast off, suggesting that 
the fungi are truly parasitic and not beneficial to the conifers. Frequently the 
invading fungi are deformed and killed by the protoplasm of the root. These 
results were obtained both with ectotrophic and with endotrophic mycorhizas. 
W. B. McDo 
found on the same root in Tilis americana. In some cases the fungus species 
involved were identified, and it was observed that the mycelia of different 
species frequently can be distinguished from one another by differences in 
color and structure. Observations made at all seasons showed that mycorhizas 
are much more in evidence in autumn, winter, and spring than in summer, and 
hence are usually annual. The fungal symbiont in ectotrophic mycorhizas, 
so far as known, is almost always a basidiomycete, whereas this is rarely the 
case with endotrophic mycorhizas. Some mycorhiza fungi can inhabit several 
hosts and the host trees also may have several different mycorhiza fungi, but 
all mycorhizal fungi cannot form mycorhizas on all mycorhizal trees. Indi- 
vidual trees or parts of trees are often without root fungi, probably because the 
proper fungus species happens to be absent. The development of the mycelial 
mantle in the ectotrophic mycorhizas checks further root growth, whereupon 
branching takes place, resulting in the characteristic coralloid aspect of the 
small root branches. The author in discussing the theories of previous workers 
agrees with Fucus (though not quoting him) that the fungi of ectrotrophic 
mycorhizas are ordinary parasites; these fungi are of no value to the trees, nor 
are they probably very harmful, since so many roots are without them, espe- 
cially in the deeper soil layers. McDovcatz is less confident concerning the 
7 Fucus, Joser, Uber die Beziehungen von Agaricineen und anderen humus- 
bewohnenden Pilzen zur Mycorhizenbildung der Waldbiume. Bibl. Bot. no. 76- 
Pp. 32. pls. g. 1911 
% McDovucatt, W. B., On the mycorhizas of forest trees. Amer. Jour. Bot. 
1251-74. pls. 4. fig. 1. 1914- 
