234 The Present State of Agriculttire 
c. Another function of the leaf opens up in like manner a large 
field of important investigation. From the pores of the leaves, 
odoriferous and other vapours, as well as liquids, exude. Need I 
remind you of the odour of a turnip field when the bulbs have 
begun to form? This and similar odours are due to the escape 
of volatile vapours from the leaves, which we have not yet sought 
to arrest or examine. The liquids which exude from leaves are 
no doubt various as the odours — their differences depending 
mainly upon the nature and the age of the plant. But there is 
reason to believe that they rarely consist of pure water. They 
hold in solution appreciable quantities of organic and saline 
matters, which, as the water evaporates from the leaf, remain 
behind upon its surface, or in its pores. These the rain washes 
off, and carries back to the soil ; and this is one of the destined 
functions of the rain in refreshing the growing plant. What are 
the substances which the plant thus discharges from its leaves ? 
What is their function in the plant? Are they indications of 
health or of disease ? In what form do they enter its roots? Are 
they necessary to the plant, and ought they, therefore, to be 
added to the soil ? Are they unnecessary, and ought they to be 
carefully withheld? In regard to these points, the practical 
tendency of which is plain, I believe, old as agriculture is, a 
single precise experiment has never yet been made. 
f. I offer you only one other illustration. You have all heard 
of the infusorial animals of Ehrenberg — those minute creatures 
which the oxy-hydrogen microscope shows to be swarming in a 
drop of stagnant water. These animals abound wherever water 
and decaying vegetable matter exist together. They abound in 
many of our soils. Do they not abound in all ? If not in all, 
then in what soils are they most abundant? Do they, like larger 
insects, prey upon living plants ? Have they anything to do with 
the sickness and death of clover ; with the perishing of young 
corn ; with the lingers and toes in turnips ? Are they in any 
way connected with the benefits derived from draining, from 
naked fallow, and from the various processes by which peat bogs 
are reclaimed ? Here is a hitherto wholly unthought of field of 
inquiry, rich in promise, the cultivation of which demands the 
united labours of the open-air experimenter, of the chemist^ and 
of the microscopical zoologist. 
T might also draw your attention to the very interesting and 
bably the excess of nitrogen, which he believed both the former substances 
to contain, might be the cause of their superior action. We may expect 
from it also a sure explanation, among other facts, of the circumstance 
that generally on the green-sand land near Newbury, and as far south as 
Salisbury, and especially in the A^ale of Pewsey, the use of bones is not 
profitable, while woollen rags, at the rate of 10 cwt. an acre, ai'e exten- 
sively applied both to the turnip and wheat crops. In the same district, 
also, nitrate of soda, for the wheat crop, is sold in large quantities. 
