424 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
In comparing the ratios of tops to roots for the 14-day period (table 4), 
it is to be noted that there is no significant difference between the mean of 
cultures of the low-nitrate and that of the medium-nitrate solutions. The 
mean of the solution with high nitrate, however, differs by a margin that is 
quite significant. The ratio is shown here to increase with the nitrate 
concentration of the solution, and it appears also that the effect may be 
noticeable during the early period of growth, even before the seedling has 
exhausted the supply of food stored within the endosperm. 
When we compare the actual dry weights in this series, the growth values 
of tops in the higher-nitrate solution are found to be greatest; in fact, the 
top weights show a variation in proportion to the nitrate concentration of 
the solutions. This is not true of roots. Using dry weights of the lowest 
nitrate solution as a basis, the top weight in the high-nitrate solution shows 
an increase of 28 percent over that in the low-nitrate solution, while the 
root weight shows an increase of only 2 percent; in the medium-nitrate 
solution, tops and roots show increases of about 15 percent each. 
The relative behavior of tops and roots of those plants harvested at the 
expiration of 21 days is still more striking than in the case of those harvested 
after 14 days. The increase in dry weight of tops in the high-nitrate solu- 
tion over that in the low is 23 percent, while the corresponding increase for 
roots is only .3 percent. Comparing these figures with 28 percent and 2 
percent respectively in the preceding series, it becomes clear that roots are 
not being influenced in any such positive way by the nitrate treatment as 
tops. The medium-nitrate solution gives an increase of 13 percent and 
10 percent respectively for tops and roots over the corresponding parts in 
the low-nitrate solution. This solution is regarded as the best balanced 
of the three and should show, therefore, more normal relationships between 
tops and roots. 
Series 3 was harvested after 28 days' growth; significant differences are 
clearly shown between the ratios expressing the variation between different 
stages of maturity, as well as between the ratios of tops to roots in the dif- 
ferent solutions. Notwithstanding the differences in mean 'ratio, there is not 
a striking difference between the total weights of cultures (tops and roots) 
of the different solutions, as a study of the table will show. This would 
indicate, of course, that the growth-producing values of the solutions do not 
differ very much. 
Another interesting fact shown in Series 3 is that while ratios of tops to 
roots have increased steadily with the nitrate concentration of the solution, 
the actual dry weights of roots in the medium- and high-nitrate solutions 
have now become less in value than those of roots in the low-nitrate solution, 
and this relationship continues during the rest of the experiment. 
The results of Series 4, 5, and 6 are given in table 4. They were har- 
vested after 35, 42, and 49 days respectively, and bring out substantially 
the same facts which have been already emphasized, namely, that at all 
