288 The Botanical Gazette. [July, 
plants were grown in natural soil, under normal atmospheric 
conditions, and also in air freed from combined nitrogen. His 
results showed a marked gain with barley in normal air, and 
somewhat less increase in air freed from fixed nitrogen. The 
N-content of seed, water added, drainage water, and crop 
were carefully determined but as he himself says, the factor 
of unsterilized soil does not exclude the possibility that lower 
organisms may have functioned in the capacity of nitrogen 
collectors. He has since repeated his experiments, *” using 
both natural and sterilized soils, and arrives at a different 
conclusion. In,unsterilized unplanted controls, having, how- 
ever, evident algal growth, a slight gain was noted. In ster- 
ilized unplanted soil and soil sown to barley a slight reduction 
was found. This corroborates Schleesing’s results and shows 
that the increase sometimes ascribed to arable land is really 
due to its living organisms. Unfortunately, the experiment 
in unsterilized soil planted to barley was lost, but the fact | 
that the sterilized soil planted with barley lost a part of its N 
shows that the supposed gain in the previous series was really 
due to soil organisms of a lower type. . : 
In Frank's last paper, already referred to, he presents his 
views in a compact and well digested form, citing experiments 
of his own, some of which are detailed for the first time, and 
critically reviewing the work of other investigators. He re- 
gards the experiments carried on in closed 
unnatural inasmuch as the conditions are so a 
plant is unable to fruit. As he claims that the nitrogeae 
similation of non-leguminous plants can only take place wie? 
the plant is thrifty and vigorous, this objection seems se 
founded. As conditions more nearly approaching pie 
the open air necessarily embrace influences that must be pi 
sidered, it would seem that the only way to settle this wk 
tion is to carry out simultaneous experiments under pi: 
conditions by both direct and indirect methods and then ©? 
late the results. 
Frank summarizes his results as follows: _ 
1. The legumes can assimilate free N wit 
vention of the symbiotic organism. + anal 
The strongest case he cites to prove this is the Experian 
cia in N-free 8 
made with four plants of Robinia pseudaca 
15 Bull. Acad. roy. de Belg. 25: 267-276. 1893. 
16 Bot. Ztg. 51: 139. 1893. 
hout the: iat 
