138 
Frank had observed that the feeding roots of certain trees were 
covered with a fungus, the threads of which forced themselves be- 
tween the epidermal cells into the root itself, which in such cases had 
no hairs, but similar bodies were found external to the fungus mantle, 
which prolonged into threads among the particles of soil. Frank 
concluded that the chlorophyllous tree acquires its nutriment from 
the soil through the agency of the fungus. Such a mode of accumu- 
lation by these green-leaved plants plainly allies them very closely 
(o fungi themselves; but inasmuch as in the cases observed by Frank 
the action of the fungi was most marked in the surface layers of soil 
rich in humus, and since this development has not been observed on 
the roots of any herbaceous plants, therefore the facts hitherto 
recorded do not aid us in explaining how the deep and strong rooted 
Leguminosee acquire nitrogen from the raw clay subsoils of Roth- 
amsted. 
In continuation of their investigations, Lawes and Gilbert have 
published a subsequent paper stating that in 1888 they began experi- 
ments in the same line as those of Hellriegel. Peas, red clover, 
vetches, blue and yellow lupins, and lucerne were sown in pots, of 
which there were four to each series. No. 1 contained sterilized 
coarse white sand; Nos. 2 and 3 contained the same sand, to which 
a soil extract was added; No. 4 contained garden soil or special 
lupin soil. Their general results were that the fixation of free nitro- 
gen only occurred under the influence of microbes in the soils that 
had been seeded with soil organisms by adding soil extract to the 
sand in the pots. They find that the Rothamsted experiments indi- 
cate that with a soil that is rich in nitrates there are far fewer nodules 
on the roots of the plants than were formed in the pots of sand con- 
taining but little nitrates but seeded with soil organisms. The 
authors suggest (1) that somehow or other the plant is enabled under 
the condition of symbiotic life to fix free nitrogen of the atmosphere 
by its leaves, a supposition in favor of which there seems to be no 
evidence whatever; (2) that the parasite microbe utilizes and fixes 
free nitrogen and that the nitrogenous compounds formed by it are 
then taken up by the plant host. On this latter supposition the 
large gain of nitrogen, as made by the leguminous plant, when grow- 
ing in a soil that is free from nitrogen but properly infected by 
microbes, becomes intelligible. (Agr. Sci., Vol. TV, p. 261.) 
As to the relations between plants and atmospheric ammonia, almost 
all agree that the plant derives ammonia from the atmosphere through 
the medium of the soil only. Berthelot. finds that vegetable soils 
usually have sufficient ammonia to’ enable them to evolve it into the 
atmosphere, but under certain conditions they can absorb this gas 
from the atmosphere. (Agr. Sci., Vol. IV, p. 295.) 
