464 
A utrition of Vegetables . 
liberated from their prisons, washed with great care, and dried. 
In this state they weighed 9 gram. [140 grs.] I filled a phial 
with them, which terminated in a narrow tube, and exposed it 
gradually to a strong heat. Thus I obtained 4 grammes, 8 dec. 
£74 grs.] of coal. But as I supposed this coal might still contain 
a little sand, I incinerated it, and found 3 gr. 3 dec. [5 1 grs.] of 
alkaline ashes. Consequently there was 1| gr. [23 grs.] of 
pure carbon. 
In a very small vessel I distilled 460 white mustard seeds* 
and from this highly hydrogenated seed I obtained only 4 giv 
£62 grs.] of coal, which lost near half its weight by calcination^ 
Hence it follows, that 460 mustard seeds acquired in close ves- 
sels upwards of a gramme [15| grs.] of pure carbon, which ap- 
peared evidently to have been formed at the expense of water, and 
probably of light. f 
Geological facts too seem to shake that theory, which ascribe®, 
the carbon found in vegetables to the small quantity of carbonic 
acid contained in the atmosphere. How indeed can so small a 
portion of this acid, scarcely amountin g to a ten thousandth 
after the experiment, its proportions appeared to be nearly the same. This 
is agreeable to the experiments of Hassenfratz, who convinced himself, 
that plants do not diminish the quantity of oxygen in a confined atmospheres 
and I am iniclined to think, that oxygen acts on plants merely as a stimulant, 
which is not indispensable, for Homberg found different seeds germinate 
in the vacuum of an air-pump. The principal cause that prevents the com- 
plete developement of plants in close vessels, appears to me to be owing 
to their abundant perspiration, which throws out the excrementitious flu- 
ids, that are so fatal to them even in the open air, as to render a certain 
space among their neighbours necessary to their vigorous growth. 
f To satisfy myself, that plants can appropriate to themselves the ele- 
ments of water, so as to constitute their different materials, only by their 
own organic action combined with that of light, I caused a given quantity 
of seed to grow in compleat darkness, and at the common temperature of 
the air. They shot out long white filam ents, at the extremity of which 
were the two seminal leaves ; but nothing more appeared. After desicca- 
tion these plants weighed less than the seeds whence they sprung : which 
appeared to be owing to their having lost carbon in this languishing siate, 
instead of acquiring it. 
But the mode of action of light on vegetables remains yet to be known. 
It appears however, that it enters into combination with them, and that to 
this combination is owing the green colour of th^ir leaves, and the variety 
of hues admired in their flowers. Yet Mr. Humboldt has found green 
plants growing in deep and dark mines, the atmosphere of which contained 
