On the Cultivated Potato. 
283 
August, September, and October : some parts of Scotland in 
July, in others not until the tubers were stored. In concluding- 
this branch of our subject I mention Mr. Malam's experiment, 
because it is suggestive ; and though I cannot of my own know- 
ledge verify the fact as stated, the experiment may be^repeated 
by any competent scientist. Moreover, the result of the ex- 
periment goes to the root of a controversy before the Potato 
Committee of the Commons as to whether mould-spores rise 
high in the atmosphere, or whether they fly no higher than a 
hedge ! Mr. Malam * personally told me in 1872, that the Hull 
Microscopical Society, about the year 1866, witnessed at his 
house the following experiment. He said : " At 7 A.M. we washed 
with distilled water a plate of glass 15 inches square, and coated 
both sides with glycerine, and elevated it in the air about 60 feet ; 
alter 6 hours it was taken down and washed on two separate 
plates with distilled water : on examining under the microscope 
we discerned spores of fungi ; the windward side contained the 
larger number." 
I have instinctively held from the first that there is such a 
thing as a balance of vegetation, and if so, atmospheric in- 
fluences must be all-important factors on the maintenance or 
disturbance of any such balance. As I expressed the idea when 
I placed my view on record in May 1875, I fancy there is such 
a thing as a balance of vegetation, that is, a proportion between 
the several organs of the plant. In warm gloomy weather, when 
-disease is exceptionally rampant, I think the leafy haulm runs 
away from the rest of the enfeebled plant ; in other words, too 
much sail is carried, and there is a general capsize and con- 
sequent wide-spread disaster. The power of the roots is said 
to be in the ratio of that of the leaves : the roots have great 
absorbing power, the leaves a low exhaling capacity. The 
evidence throughout shows that over-luxuriance, from whatever 
cause, is highly favourable to the disease : in Bengal it is re- 
corded the haulm grew so high, it spent the plant. This balance 
of vegetation theory, as an essential part of my retrospect, for 
what it is worth, I simply broach and submit. 
Superior vitality, we know, is an attribute for a time at 
least of certain varieties of the potato that more or less resist 
disease. Liebig adopts the vital power theory. The Polish 
letter from the Consul there to Lord Palmerston, and dated 
October 16, 1846,t is in my view particularly interesting and 
suggestive ; Poland completely escaped the general European 
-destruction. That country, as regards wholesale cultivation and 
* The statement was subsequently printed. ' The Potato Disease, Cause and 
ilemedy.' By John Malam, Esq., Scarborough, Theakston, 1873. 
t 'Journal,' R. A. S. E., vol. vii. p. 67G. 
