208 BOTANICAL GAZETTE [OCTOBER 
The injury to these seedlings was relatively great, therefore, but 
this was not the case with seedlings having large root growth 
It appears that there are several reasons that can be offered as an 
explanation for this relatively good growth obtained from the cul- 
tures with large roots grown in solution no. 2. The roots of these 
cultures, presumably because of their age, had much suberized 
tissue. This could inhibit the entry of excessive amounts of salts. 
It could also cause the precipitation of some of the salts in the 
root mass without doing injury to the plants, and, also in a 
selective way prevent or retard the absorption of toxic ions. On 
the other hand, this large root system was beneficial to the plant 
growth in this poor solution, in that it still permitted sufficient 
absorption of the essentialions. The greater surface exposed to ab- 
sorption of nutrients, therefore, could compensate for the decrease in 
the rate of intake of essential nutrients per unit area of root surface. 
Results obtained from solution no. 3 show that the plants having 
comparatively small root systems, when placed in the solution, pro- 
duced approximately 90 per cent more dry weight than did the 
other class of cultures grown in this same kind of solution. The 
dry weight of the cultures of class B was also more than four times 
larger than that of the corresponding cultures of solution no. 2. 
The growth obtained from class B cultures in this solution (no. 3); 
in which MgSO, composed eight-tenths of the total salt concentra- 
tion, must be considered as very good. Had growth conditions pre- 
vailed that would have induced a higher rate of transpiration, these 
cultures would not have attained to the value they held in this test. 
It is to be noted that these cultures had the lowest percentage of 
dry matter in the roots of all sets, being 11.7 per cent of the total 
growth obtained, and constituting a very low value for wheat plants 
six weeks old. One effect of this solution was to retard root growth 
in the cultures of class B as compared with the growth of top. 
Under conditions of excessive transpiration this condition would 
have acted harmfully to the plants. As it was, the cultures of class 
B having the smallest root systems as compared with the tops of the 
plants appeared to have been the most efficient, if ratio of root 
growth to top be taken as the criterion. 
The dry weight of all the cultures having large root systems 
(class A) when placed in the three different kinds of solutions were 
