he water. It is this salt which gives foecundity to all
things: and from this salt (rightly understood) not only all vegetables,
but also all minerals draw their origine. By the help of plain
_salt-peter_, dilated in water and mingled with some other fit earthy
substance, that may familiarize it a little with the corn into which I
endeavoured to introduce it, I have made the barrenest ground far out-go
the richest, in giving a prodigiously plentiful harvest. I have seen
hemp-seed soaked in this liquor, that hath in due time made such plants
arise, as, for the tallness and hardness of them, seemed rather to be
coppice-wood of fourteen years' growth at least, than plain hemp. The
fathers of the Christian doctrine at Paris still keep by them for a
monument (and indeed it is an admirable one) a plant of barley
consisting of 249 stalks, springing from one root or grain of barley; in
which they counted above 18,000 grains or seeds of barley. But do you
think that it is barely the salt-peter, imbibed into the seed or root,
which causeth this fertility? no: that would be soon exhausted and could
not furnish matter to so vast a progeny. The salt-peter there is like a
magnet, which attracts a like salt which foecundates the air, and gave
cause to the Cosmopolite to say there is in the air a hidden food of
life."[3]

_Duhamel and Hales._

The names of the French writer, Duhamel, and of the English, Stephen
Hales, may be mentioned in passing as authors of works bearing on the
question of vegetable physiology. Both of these writers flourished about
the middle of the eighteenth century. The writings of the former
contained much valuable information on the effects of grafting, motion
of sap, and influence of light on vegetable growth, and also the results
of experiments which the author had carried out on the influence of
treating plants with certain substances. 'Statical Essays, containing
Vegetable Staticks; or an Account of some Statical Experiments on the
Sap of Vegetables, by Stephen Hales, D.D.' (2 vols.), was published in
London in 1738; and contained, as will be seen from its title, records
of experiments of very much the same nature as those of Duhamel.

_Jethro Tull's Theory._

Some reference may be made to a theory which created a considerable
amount of interest when it was first published--viz., that of Jethro
Tull. The chief value of Tull's contribution to the subject of
agricultural science was, that he emphasise