1906] TRANSEAU—BOGS 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 to 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 30°™ test tubes were set 
upright, and 8°™ of glass beads were poured into the bottom of 
each. Into onea 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°™ 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.® 
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 (1) the mycor- 
hizas develop only in poorly aerated siento (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 
