S3 
of Nature ; to cause the Hyacinth; Narcissus, and other bulbous plants, to 
germinate much sooner than they otherwise would have done. 
E X P E RIM E N T XLII....XLY. 
Pursuing the inquiry, Humboldt found that metallic bodies simply did 
not promote germination, but that metallic oxydo favour it, and that, in the 
exact proportion of the degree of oxydation* of the metal. 
Yon Uslab, has confirmed these experiments, and observes that, even in 
the oxyd of lead (litharge), he found that plants grew very well, and better 
indeed than in pure earth. 
And the learned Dr. Darwin in his Phytologia^ mentions, that he has 
* Not only do all metals compared with each other absorb different quantities of oxygen to satu¬ 
rate them in their combustion by the contact of air, but each metal considered separately absorbs dif¬ 
ferent proportions, and stops at various points of oxydation, according to the degree of temperature to 
which it is raised. Thus tin, lead, copper, iron, change colour and assume the tints of the rainbow, 
at the first degree of fire to which they are exposed in contact with the air; Lead first becomes a grey 
oxyd, next yellow, and lastly red; Mercury passes from black to white, from white to yellow, and 
from yellow to red; Iron, at first a black oxyd, becomes next green, then brown, and ultimately 
white; Copper is at first a brown oxyd, from which it changes to blue, and its last degree of oxyda¬ 
tion imparts to it a green colour. 
f The Phytologia of this able writer arose from a circular letter sent round by the Board of Agri¬ 
culture, proposing queries respecting numerous points, relative to the growth and cultivation of 
plants, and it contains a concise account of all the most important discoveries, that have any con¬ 
nexion with the subject of Botany, and these are so nicely arranged, and digested, with new obser¬ 
vations from the author, as to form a work, that may certainly boast of being the first Philosophic 
Treatise upon so interesting a branch of Science. My New Illustration of the Sexual System of 
Linnjeus, was begun long before the appearance of Dr. Darwin’s elaborate work, and the plan pub¬ 
licly proposed, and I have to rejoice that our respective performances do not interfere, but must 
mutually advance each other. Dr. Darwin addresses his readers, as already conversant in botany and 
adepts in the new chemistry. My work supposes in my readers a total unacquaintance with all kind 
of chemical and botanical knowledge, and I expatiate on the several subjects I have to treat of, and 
lead my readers, step by step, from lesser to higher flights, enforcing all the while my instructions, by 
plates, which from their fine execution, (as is universally allowed,) “ may be as a substitute for the plants 
themselves,” which I conceive to be the readiest way of attaining a knowledge of the useful and 
delightful science of Botany. For, as the great Rousseau justly laments to the Duchess of Portland, 
in his Letters, “ No such work was to be found, in his time, and as plants bloomed at different 
seasons, and could not always be procured, to acquire a knowledge of Botany from the Book of Na¬ 
ture was a tedious and almost insurmountable attempt.” In a few words, my work is chiefly elemen¬ 
tary, Dr. Darwin’s wholly philosophic; and I take this opportunity of expressing the great obligations I 
owe to the Phytologia, as well as to Dr. Darwin’s two immortal poems, the (Economy of Yege- 
t\tion, and Loves of the Plants, which have so often served to enliven the heads ot the several 
sections, by furnishing an appropriate motto. As an excuse for some liberties taken with the text, 
vide note *, page 41 , I must beg leave to add also, that the notes of the Botanic Garden contain 
a fund of useful erudition. Indeed, all Dr. Darwin’s writings are intrinsically excellent, and superior 
to my feeble praise. 
