326 • Nature and Cause of the Potato Disease. 
of alumina and potash) prevent the formation of the black colour, 
and consequently putrescence also. 
Sulphuric, hydrochloric, nitric, oxalic, tartaric, and acetic acids, 
moderately diluted with water, soften cut slices of potato, and for 
a time prevent putrefaction. But after an immersion of two or 
three months the potato becomes disorganized, but does not 
blacken although exposed to the atmosphere for three or four 
months, but yet decomposition ensues notwithstanding. Tannin, 
tannic and gallic acids, and alum, harden slices of potato and 
prevent putrefaction : they have great antiseptic properties, so far 
as regards the potato. 
10. The adaptation of the Plant to certain Conditions. 
In the arrangement of the potato plant we have seen that it 
possesses a considerable extent of roots and numerous absorbents, 
and that ihe roots are so contrived that thev lie below the stolons 
to which they are attached, and thus place the stolons and tubers 
in higher and drier soil than themselves. This is a striking ar- 
rangement of parts ; and the inferences deducible from it are, 
1st, That the roots, having numerous absorbents, are intended for 
a comparatively dry situation ; and, 2ndly, That the tubers are 
intended for a drier situation than the roots themselves. A plant 
formed for a moist or damp soil has no need for the thousands of 
absorbents that the potato possesses, because if the whole of them 
are to be usefully employed they must be placed in a situation 
where they have to seek moisture, and not where they are em- 
bedded in it. Contrast the potato with the turnip, and this will 
be apparent. In the turnip, but few roots and spongioles appear, 
and it needs moisture in its culture, while, on the other hand, the 
potato possesses numerous absorbents ; and we know by expe- 
rience that it thrives best in comparatively dry situations. The 
foliage of the two plants is as characteristic of their nature as the 
roots themselves, and furnish us with additional evidence of their 
wants, and the means by which nature has contrived to supply 
them. In the potato the foliage is high, and evaporation from 
the soil is but little impeded by it; while in the turnip it is low 
and wide-spreading, and evaporation is consequently much im- 
peded by such an arrangement. The structure of these plants is 
therefore widely different, and had we no experience of their 
natures we might infer from their organisms only that they are 
not suited to the same circumstances, and that they require 
different situations to flourish in. 
The turnip has but few roots to absorb moisture and inorganic 
matter, it therefore demands to be placed in a suitable soil, in a 
moist situation. The potato has many roots and numerous ab- 
sorbents, and it can thrive where the turnip would languish and 
