302 
RICHARD M. HOLMAN 
when they are growing in sawdust or sphagnum which is compressed 
than when they are surrounded by these media in a very loose con- 
dition, provided, of course, that, as in my experiments, the proportion, 
by weight, of water to the medium is in both cases the same. As 
previously mentioned in connection with the discussion of Hofmeister's 
theory, any attempt to explain the differences in behavior of the 
roots in different media as due to differences in water content appears 
to be finally contradicted by the fact that roots in water behave very 
much as do those in moist air. It is conceivable however that neither 
the condition of water shortage prevailing in moist air nor the rela- 
tively limited gas interchange in the case of roots submerged in water 
is favorable to an acute permanent curvature. In this connection I 
performed experiments with roots which were permitted to curve in 
response to gravity while growing in earth containing water in different 
proportions. For this purpose sieved garden earth was employed 
which was dried in thin layers for four days at 50° C, after which it 
had lost 28 percent of its weight. Roots planted in this dried soil 
soon died. The soil was then divided into three lots and water was 
added to these in the proportions of 20 percent, approximately 30 
percent and 40 percent of the dry weight. Six of the eighteen roots 
of Vicia faba var. equina used, were planted in each of these three 
lots of earth in Sachs's boxes. All of the roots curved promptly into 
the perpendicular. The mean rate of downward curvature was, as is 
shown by the measurements in Table VI, nearly the same for all three 
cultures. 
In the case of these cultures and those of other similar experiments 
which I have performed, the curvatures in two lots of earth of which 
one contained twice as much water as the other (in this case 20 per- 
cent and 40 percent of the air dry weight) showed no difference in 
intensity. In cultures in loose moist sawdust and in moist sawdust 
so compressed that a given volume contains twice the amount of 
water in the same volume of the loose sawdust, the curvatures are of 
entirely different form. 
It seems certain that, although differences in the amount of 
moisture in the medium may not be without influence upon the geo- 
tropic curvature, this factor cannot explain the great difference in the 
secondary curvature of roots in air or very loose sawdust and in earth 
or compressed sawdust. Furthermore roots in air, even when they 
are so frequently sprayed that they are constantly covered with a 
