BULLETIN OF THE BUSSEY INSTITUTION. 283 
to avail itself of the stores of less accessible nitrogen that are con- 
tained in the soil, or that a certain amount of one of the active forms 
of nitrogen is needed for the performance of some special physiological 
work within the plant, while the soil-nitrogen, or the products of its 
decomposition, may be perfectly competent to do the other kinds of 
work, or indeed most of the work that is required of that element in 
the process of building a plant. 
The latter view would appear to derive some support from the 
familiar fact that some kinds of plants, such as the cereals, have far 
more need of the active forms of nitrogen than other plants of a 
different physiological habit, such as clover and turnips. It agrees, 
moreover, with certain differences in the behavior of plants towards | 
solutions of nitrates, ammonium salts, and some other soluble forms of 
nitrogen, that have been repeatedly noticed in experiments made by 
way of water-culture or of sand-culture. The nitrates favor the 
growth of plants. both young and old; but it has been found that 
plants reared by these methods have in general little liking for the nitro- 
gen of ammonia compounds during the earlier stages of their growth. 
When very young, it appears to be difficult for the plants to assimilate 
the ammonia or even to bear its presence ; but as they grow older this 
difficulty disappears or is very much lessened. ‘The remark applies 
particularly to the phosphate of: ammonia and nitrate of ammonia, 
by means of which plants have been successfully grown by the methods 
in question. The hurtful influence of sulphate of ammonia and chloride 
of ammonium, when used by themselves in sand or water culture, is a fact 
of another order, that is readily explained, since these salts are decom- 
posed by the roots of plants in such wise that corrosive acids are pro- 
duced which destroy the plants.* But this explanation fails to account 
for the behavior of the other ammonium salts, and especially that of 
nitrate of ammonia. I have myself noticed in experiments made with 
this salt curious anomalies analogous to those mentioned by Hell- 
riegel.t ; 
It would be of scientific interest, in this connection, to determine, 
by careful experiments, devised to that end, whether the minute traces 
of active nitrogen naturally contained in the rain-water with which the 
soils in my experiments were moistened, could possibly have had any 
* See Johnson’s “‘ How Crops Grow,” pp. 170-171. 
t In Steeckhardt’s “‘ Chemische Ackersmann,” 1873, 19. 223. 
