MR. BERKELEY ON THE POTATO MURRAIN. 19 



Decaisne, Desmazieres, Duchartre, Morren of Rennes ; Phi- 

 lippar and Pouchet in France ; Drs. Kiitzing- and Munter, in 

 Germany ; and in the Britisli dominions, Drs. Kane, Playfair, 

 and Lindley, Dr. Bellingham, Mr. W. Andrews, and Mr. G. 

 Phillips. The matter is diffigrently expressed by different 

 parties : some speaking principally of excessive moisture ; 

 others of alternations of heat and moisture ; otliers of the pecu- 

 liar electric phenomena ; and all, more or less, of the surcharge 

 of tlie cellular tiss\ie with moisture. It will not be necessary to 

 examine the views of each separately, because they all tend essen- 

 tially to the same point. Those of M. Decaisne, unfortunately, 

 have at present only been partially stated. I regret much that 

 liis memoir Avill not appear until these observations are in the 

 printer's hands. 



Dr. Lindley stated the matter very clearly in the ' Gardener's 

 Chronicle ' for August 23, in a passage whicli I proceed to copy. 

 It is to be remembered that it was written at an eariy stage of 

 the inquiry, but his views have suffered scarcely any alteration, 

 notwithstanding the great attention he has since given to the 

 subject. 



" The cause of this calamity is, we think, clearly traceable to 

 the season. During all the first weeks of August the tempera- 

 ture has been cold, from two to three degrees below the average 

 — we have had incessant rain and no sunshine. 



" The potato absorbs a very large quantity of water. Its 

 whole construction is framed with a view to its doing so ; and 

 its broad succulent leaves are provided in order to enable it to 

 part with its water. But a low temperature is unfavourable to 

 the motion of the fluids or to the action of the cells of the plant ; 

 and, moreover, sunlight is required in order to enable the water 

 sent into the leaves to be perspired. In feeble light the amount 

 of perspiration from a plant is comparatively small ; in bright 

 sunshine it is copious : in fact the amount of perspiration is in 

 exact proportion to the quantity of light tliat falls upon the leaf. 

 At night or in darkness there is no appreciable action of this 

 kind. During the present season all this important class of 

 functions has been deranged. The potatoes have been compelled 

 to absorb an unusual quantity of water ; the lowness of tempera- 

 ture has prevented their digesting it, and the absence of sunlight 

 has rendered it impossible for them to get rid of it by perspira- 

 tion. Under these circumstances it necessarily stagnated in the 

 interior ; and the inevitable result was rot, for a reason to be 

 presently explained. If the first days of July had not been sud- 

 denly hot, it would not have happened ; and perhaps it would 

 not have occurred had the temperature been high instead of low, 

 even although the sun did not shine and rain fell incessantly. 



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