ME. BERKELEY ON THE POTATO MTIKEAIN. 21 



causes mentioned by Dr. Lindley as producing the putrefaction 

 of the stems, even if it be not considered as tlie immediate cause, 

 tiie Botrytis wouhl be concurrent in preventing the perspiration 

 of the excess of moisture. For not only does the mycelium 

 block up in great measure the loose tissue which gives a passage 

 to the fluid, but more or less completely the stomata also by 

 which the vapour passes. 



As regards electric phenomena, though they are known to 

 have a most important influence on the production of fungi, 

 it is far from clear that they have much effect on phsenogamous 

 plants. The experiments lately made on the influence of elec- 

 tricity on vegetation seem to show that it is very small. 



Besides the objection stated by Dr. Lindley as capable of 

 being brought forward against his views, it may be urged that 

 the fact of the disease not being peculiar to the year 1845, but 

 having been excessively destructive in 1844, and more or less so 

 in preceding years, greatly militates against the notion of its 

 being due to the peculiar season. For it cannot be asserted that 

 there was much similarity between 1844 and 1845. And, taking 

 the experience merely of 1845, and the various times at which 

 the disease made its appearance in different parts of the country, 

 the same conditions did not exist in all cases. In many districts 

 it made its appearance during tlie very dry weather at the end of 

 August and beginning of September. Besides, it does not appear 

 that differences of soil have had much weight in the progress of 

 the disease. In many districts it has been found that the pota- 

 toes in the driest soils have been affected most. In the fens* of 

 Cambridgeshire it has been observed generally that those spots in 

 which the water was not perfectly drained, suffered much the least, 

 and similar accounts have been received from other quarters. 



I think, too, it may be doubted whether the season, though 

 extremely cold and ungenial, has really been more wet than 

 usual. f Dr. Bell Salter, in a late number of the ' Gardener's 

 Chronicle,' writes as follows from the Isle of Wight : — " In this 



* It perhaps may be objected here that the water being impregnated with 

 peat, acted as a preservative. The experience, however, of various districts 

 shows that the peculiar nature of the soil had, in general, little influence on 

 the disease. No districts suffered more than the dry parts of the fens. 



t It appears from observations made at Chiswick, as reported in the 

 ' Annals of Natural History,' that the quantity of rain from May to Septem- 

 ber inclusive was below the average of the last eight years : the average 

 quantity of raiu during those months being 11-20 inches; while during the 

 same period in 1845 it was IT 12. Neither was the rain in any one month 

 greatly above the average. 



May. June. July. August. September. 



Average of Eight Years 2-02 2-26 2-10 2-2G 2-52 



1845 . . . 2-89 1-36 2-31 2-79 1-77 



