344 Ward. — Recent Pitblications bearing on the 
others close beside these do worse ; and yet others may 
never pass through the starvation-period. It occurs not 
rarely (and this is expressly insisted upon) that of two peas 
growing side by side in the same vessel, the one starves and 
the- other succeeds in the highest degree. 
Now, since it is impossible to assume, in earnest, that peas 
have the power of growing without nitrogen in the soil, 
and at one time to succeed and at another to fail, the only 
explanation is that the above extraordinary behaviour of 
the control-plants in well-arranged experiments, is that there 
is, in addition to the known and carefully regulated factors, 
some unknown co-operating factor, which depends on ac- 
cidentals and which exists outside the culture-vessels. 
Hellriegel then proceeds to describe the following experi- 
ment. Four vessels were filled with soil devoid of nitrogen, 
and peas put in and allowed to germinate ; the vessels were 
then placed under four glass bell-jars, enclosed, and joined 
by tubes, and the whole so arranged that a constant stream 
of air was drawn through from No. i to No. 4. Absorption- 
vessels were placed between each pair of bell-jars, and matters 
so arranged that the air passed into No. 1 unaltered, but, 
before entering Nos. 2, 3, and 4, was deprived of ammonia 
and nitric acid. The pea-plants were each about 15 cm. 
high, and had passed successfully through the above-named 
starvation-phase, and entered into the second lease of ex- 
istence. This continued under the bell-jars, and, in short, 
all the plants flourished, and attained an average height of 
120 cm., and had entered upon the flowering and fruiting 
stage when the experiment was stopped. The results were — 
No. 1 = Ordinary atmospheric air, yielded 13*6 gr. of dry 
substance in the straw, and 3-4 in the roots, = 17 in all. 
No. 2 = Purified air, yielded 14*6 in straw, and 3-5 in roots, 
= 18-1 in all. 
No. 3 = Purified air, yielded 19-1 in straw, and 3*9 in roots, 
= 23 in all. 
And the author states that the observations lend no pro- 
bability to the idea that the small traces of combined nitrogen 
