1906] TRANSEAUBOGS OF THE HURON RIVER VALLEY 33 



In order to get at the conditions which favor or cause the develop- 

 ment of mycorhiza, cultures of Larix were made in loose sphagnum, 

 sand, undrained sphagnum, etc. The roots in the many other cul- 

 tures previously noted were also carefully watched. It has been 

 found without exception that where the plants were grown under 

 properly aerated soil conditions, normal roots developed in place of 

 the mycorhiza. That the acidity of the bog water has nothing t'o do 

 with the production of mycorhiza is shown by the fact that in water 

 cultures of the same acidity as the solution in the undrained peat, the 

 plants develop normal roots. In the case of roots developed in loose 

 sphagnum, sand, and moist air, an abundance of root hairs were pro- 

 duced. The normal roots in Larix have a diameter about three 

 times that of the mycorhiza, so that when they begin to develop they 

 appear like white pendants from the dark brown mycorhiza. That 

 mychoriza will not develop in a well-aerated substratum was further 

 tested by the following experiment: Two 3o cm test tubes were set 

 upright, and 8 cm of glass beads were poured into the bottom of 

 each. Into one a glass tube, at whose end were several small open- 

 ings, was passed to the bottom. The upper part of the tube was 

 connected with a gasometer. Upon this foundation of beads, three 

 plants of Larix were planted in a 5 cm layer of peat in each tube. 

 The water level in the two tubes was kept just at the surface, bog 

 water being used throughout. Air was then forced from the gas- 

 ometer to the bottom of the one tube and allowed to pass slowly 

 through the beads and peat. When the experiment was started, all 

 of the plants possessed only mycorhiza. In the course of a week the 

 aerated plants began to develop normal roots. The experiment was 

 continued for six weeks. The unaerated plants developed only 

 mycorhiza, while those which were aerated developed normal roots. 8 

 The growth of mycorhiza is exceedingly slow, and the fungus grows 

 with the root. The development of the above ground parts cor- 

 responds to the root development. The plants which produce normal 

 roots have longer shoots, and longer, thicker leaves. 



It seems evident, in the case of Larix at least, that (i) the mycor- 

 hizas develop only in poorly aerated substrata; (2) their growth is 



8 In the case of a number of the plants of Larix grown in the undrained peat 

 in previous experiments, one or two normal roots were developed just at the surface 

 of the substratum. 



