635 



tis as this has been ably done by Mr. Berkeley, Taking these circum- 

 stances into consideration, the absence of the fungus from some even of 

 the recent spots, the fact that the Botrytis only appears on the dead, 

 half-dead, or even decaying portions of the leaf, I think that I am 

 justified in concluding that the Botrytis is not the cause, but the con- 

 sequence of the death of some portion of the tissue of the leaf. It 

 seems to me quite as rational to believe that the sporules of this fun- 

 gus floating in the atmosphere affix themselves to the dying leaf, and 

 finding thus a fitting nidus for their development, arrive at maturity, as 

 to suppose that they are absorbed and carried by the juices to every 

 part of the plant, ft would be quite as rational to believe that the 

 sporules of any of the common moulds, were circulated in the tiuids 

 of an animal whose flesh, after a few days' exposure to the atmos- 

 phere, is found to be covered by them. The experiments of Schultzc 

 have shewn that unless these sporules, which from their excessive 

 minuteness float easily in and are diffused through the air, are ad- 

 mitted to animal, or vegetable substances undergoing decay, no de- 

 velopment of Mucors or animalcules can occur. I conclude therefore 

 that the appearance of the Botrytis is a secondary consequence of the 

 disorganisation and loss of vitality of some portion of the cellular 

 tissue of the leaf. 



From the leaf itself we now proceed in a downward course to the 

 petioles and stem, and here we find marks of disease. The petioles 

 become brown, some portions retaining their normal or healthy appear- 

 ance. The diseased parts are flaccid, more transparent and more 

 watery than natural, but their sections do not show any appearance of 

 fungus, or at least I have not been able to detect any traces of either 

 mycelia or perfect fungi. The stem itself is subject to similar changes ; 

 but being more bulky and retaining its moisture longer, the color is 

 deeper and becomes almost black ; decay goes on, the cellular tissue 

 of the pith is disintegrated or destroyed, and fungi are then said to 

 be found in the hollow. In the field of potatoes I examined at Croy- 

 don some days since, I could not see any stems in this state, and 1 

 have since been favoured by my friend Mr. Cooper, with some of the 

 most diseased stems that could be found in a field severely affected 

 with the disease ; but in these no appearance of fungus could be dis- 

 covered. It is extremely probable that in a very advanced stage of 

 decay, and perhaps later in the present season, such fungi will be 

 found, as they will also on almost every decaying stem of an 

 herbaceous plant. At all events 1 can affirm that so far as my inves- 



