to the air; and which, if
they went on breathing, and their breath were not made into trees, would
poison them, or rather suffocate them, as people are suffocated in
uncleansed pits, and dogs in the Grotta del Cane. So that you may look upon
the grass and forests of the earth as a kind of green hoar-frost, frozen
upon it from our breath, as, on the window-panes, the white arborescence of
ice.

13. But how is it made into wood?

The substances that have been breathed into the air are charcoal, with
oxygen and hydrogen,--or, more plainly, charcoal and water. Some necessary
earths,--in smaller quantity, but absolutely essential,--the trees get from
the ground; but, I believe all the charcoal they want, and most of the
water, from the air. Now the question is, where and how do they take it in,
and digest it into wood? {47}

14. You know, in spring, and partly through all the year, except in frost,
a liquid called 'sap' circulates in trees, of which the nature, one should
have thought, might have been ascertained by mankind in the six thousand
years they have been cutting wood. Under the impression always that it _had
been_ ascertained, and that I could at any time know all about it, I have
put off till to-day, 19th October, 1869, when I am past fifty, the knowing
anything about it at all. But I will really endeavour now to ascertain
something, and take to my botanical books, accordingly, in due order.

(1) Dresser's "Rudiments of Botany." 'Sap' not in the index; only Samara,
and Sarcocarp,--about neither of which I feel the smallest curiosity. (2)
Figuier's "Histoire des Plantes."[18] 'Seve,' not in index; only Serpolet,
and Sherardia arvensis, which also have no help in them for me. (3)
Balfour's "Manual of Botany." 'Sap,'--yes, at last. "Article 257. Course of
fluids in exogenous stems." I don't care about the course just now: I want
to know where the fluids come from. "If a plant be plunged into a weak
solution of acetate of lead,"--I don't in the least want to know what
happens. "From the minuteness of the tissue, it is not easy to determine
the vessels through which the sap moves." Who said it was? If it had been
easy, I should have done it myself. "Changes take place in the composition
of the {48} sap in its upward course." I dare say; but I don't know yet
what its composition is before it begins going up. "The Elaborated Sap by
Mr. Schultz has been called 'latex.'" I wish Mr. Schultz were in a hogshead
of it, with