436 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
containing the solutions were plugged with cotton and sterilized for 30 
minutes at 15-pounds' steam pressure. 
Seeds 
The seeds for the cultures were carefully selected on the basis of their 
vigor and uniformity. They were first sterilized for 4 hours by the calcium 
hypochlorite method developed by Wilson (34) in 1915, and after being 
washed with sterile water they were transferred for germination to sterile 
agar in plugged 50-cc. vials. A word might be said here with reference to 
the Wilson solution as a sterilizing medium. A claim for this method which 
would highly recommend it is that seeds may be effectively transferred 
from it directly to the germinating medium without washing in sterile 
water. When one is dealing with individually weighed and recorded seeds, 
the percentage germination of these seeds becomes a very important factor 
both from the standpoint of accuracy of results and from that of labor 
involved. It is the writer's experience that unless the grains of corn are 
washed thoroughly on transference from the calcium-hypochlorite solution 
to an agar germinating medium, the percentage of germination is greatly 
reduced, sometimes as much as 60 percent. 
Cultures were grown in the greenhouse in a dark chamber specially 
constructed to allow for the free circulation of air. 
In Experiment V, the tips only of corn roots were employed. When 
the radicle had reached a length of 2 to 3 cm., it was removed with a sharp 
scalpel, under sterile conditions, dropped into the sterile culture solution, 
and set away in the dark chamber for growth. 
The results of two series of 20 and 44 days' growth respectively are 
presented in table 8. A third series was conducted, but as several cultures 
in the low- and medium-nitrate solutions became contaminated, comparative 
results are not possible, though the results in the high-nitrate solution both 
as to green and as to dry weight are essentially the same as those reported 
in Series i. Eight cultures constituted a series. 
The results of Series i (Experiment V), in which root tips only were 
used, show clearly, as far as green-weight determinations are concerned, 
that there is an increase in weight when the amount of nitrates in the 
solution is increased. The medium-nitrate solution appears slightly more 
efficient here, as was the case with cultures of entire plants growing in the 
mineral-nutrient solutions alone. 
The dry-weight determinations for the twenty-day period do not, at 
first glance, appear to give such positive evidence as those of green weight of 
an increased growth as the nitrate content of the nutrient solution is in- 
creased, since there are such small differences among the weights for this 
period; but the fact has already been demonstrated and pointed out that 
dry-weight determinations are by no means safe criteria of growth of plants 
