168 On the Prevention of Curl and Dry-Rot in Potatoes. 
and in suitable soil, taken up a few weeks later, will be found 
light and mealy. This is probably owing to the deposition of 
starch in the tuber by the descent of the sap when the growth of 
the plant has ceased, and is apparently analogous to the very 
similar process described by Professor Liebig * as taking place in 
all perennial plants. " All the carbonic acid which the plants 
(sjieaking of perennials only) now absorb is employed for the 
production of nutritive matter for the following year. Instead of 
woody fibre, starch is formed, and is diffused through every part 
of the plant by the autumnal sap." To remove every doubt on 
the subject, however, I took up portions of two kinds of potatoes 
growing in very different situations, and sent a ripe and unripe 
sample of each to Mr. Spence, analyzing chemist, York, merely 
numbering the samples, and requesting to know the per centage 
of starch in each. The result was as follows : — 
Remaindrr, 
Water. Starch. consisting of 
dry tibre, &c. 
No. 1. Black kidneys, unripe . . . 68-7 17-7 13-5 
No. 2. Ditto, ripe 72-0 17-9 10-0 
No. 3. Round reds, unripe . . . . 69-8 15-1 15-0 
No. 4. Ditto, ripe ...... 73-8 17-9 8-2 
The proportion of water in the unripe samples here seems to 
be about 4 per cent, less than in the ripe samples, but this was 
probably owing to the unrij)e sam])les having been taken up some 
weeks earlier, and kept out of the ground until the others were 
considered ripe enough. If this were taken into account, the 
increase of starch in the interval would be still more marked. 
As it stands, however, the altered proportions of the principal con- 
stituents are remarkable. Neglecting the water as unconnected 
with the present inquiry, we find that the proportion of starch to 
the other solid matters is as 177 : 135 in the unripe kidneys, but 
as 179 : 100 in the ripe ; or reducing both to a common measure, 
we have — 
Starch : other solid matters : : 131 : 100 m the unripe kidneys. 
: : 119 : 100 in the ripe ditto. 
In the round reds, reducing as before to a common measure — 
Starch : other solid matters : : lOOf : 100 in the unripe reds. 
:: 2164- : 100 i" the ripe ditto. 
In each case it thus appears that the proportion of starch to the 
other solid matters had increased considerably in the interval 
which had elapsed between taking up the ripe and unri})e parcels. 
The remark will here be probably made, that though an increase 
of starch has undoubtedly taken jilace, yet the quantity present 
was considerable before, why then should an addition to it injure 
the germinating power of the set ? To answer this question it is 
* Organic Chemistry of Agriculture, p. 124. 
