342 Ward. — - Recent Publication bearing on the 
is directly proportional to the quantity of nitrates employed 
(so long as the maximum is not surpassed). 
Moreover, nitric acid is no doubt the only available source 
of nitrogen for the Gramineae ; when other nitrogenous com- 
pounds are offered, they only become available so long as 
they are oxidised to nitric acid compounds. Thus the 
development of the Gramineae is in direct relation to the 
quantity of nitric acid present in or manufactured in the soil. 
Hellriegel then proceeds to show that experiments with 
leguminous plants yield totally different results. 
If peas are allowed to germinate and grow in soil devoid 
of nitrogen, the result is astounding. In the same kind of 
soil deprived of nitrogen, in which grasses always pass into 
the starved condition above described, the peas flourished and 
yielded a large increase . Thus, from small culture-vessels, 
20 cm. high and containing each four kilos of sand, the author 
got the following results. 
In 1884, 13-947 gr. of peas (seed) yielded 28-483 gr. of dry 
substance above ground. 
In 1885, 11-710 gr. of peas gave a yield (above ground) of 
27-816 gr. 
In 1885, also, 12-426 gr. peas yielded 33-147 gr. of dry 
substance. 
And in 1886, 8-956 gr. peas gave 20-372 gr. dry substance. 
Moreover, the plants were normally growing, and even vigorous, 
and Hellriegel points out that such a yield as 33 gr. of dry 
substance from the same sources could not be obtained with 
barley even if nitrates were added. 
Now comes the question, whence did the peas obtain the 
nitrogen necessary for this rank growth ? ‘ There is ap- 
parently but one definite answer — from the air ! ’ The soil 
was a pure quartz sand, repeatedly washed ; the nutritive 
mixture contained no nitrogen compound ; the distilled water 
was specially prepared, and free from ammonia or nitric 
acid. Even if it be supposed that traces of any nitrogen 
compound did fall into the vessels, the author points out that 
it would be out of account when we consider the large yield 
