470 



structure of the potato, of the brown granules, and of Botrytis infes- 

 tans, &c.). 



Dr. Greville, in making a few observations, commenced by paying 

 a high compliment to the talents of Mr. Goodsir, and the general ac- 

 curacy of his microscopical researches. "With reference to that gen- 

 tleman's theory," said Dr. Greville, " I see nothing improbable in the 

 potato-murrain being analogous to epidemic diseases in the animal 

 kingdom. In fact, the analogies between the two great kingdoms of 

 organized matter are so many and so strong, that he might reasonably 

 look for much similarity among some of the phenomena exhibited in 

 both, with regard to disease. Like epidemics in the animal world, 

 the one under consideration has appeared almost simultaneously in 

 various and remote parts of the globe; a fact which seems to indicate 

 some atmospheric influence. The real cause, as in the case of all 

 epidemics, is involved in the greatest mystery. Possibly a union of 

 conditions may have taken place, favourable to the development of 

 the fungus which appears to be invariably present. We all know 

 that iu the germination of monocotyledonous and dicotyledonous 

 seeds, a union of three conditions is essential : the presence of air, 

 warmth and moisture. If any one of these conditions be wanting, the 

 seed will not germinate, but, if otherwise favourably circumstanced, 

 will remain in a dormant state for an indefinite period. In like man- 

 ner I think it not improbable that certain conditions — one or more 

 of them being of a meteorological character — may have combined in 

 the course of the past season to promote the growth of the potato- 

 fungus. The question has been asked. How do the spores of the 

 fungus obtain access to the vegetable tissue ? This at present is a 

 matter of mere speculation. They are excessively minute ; and it 

 has occurred to me, that they, as well as the spores of other of the 

 minute fungi, may at all times inhabit the tissue of those species of 

 plants to which they are respectively peculiar, without, under ordi- 

 nary circumstances, deranging the vegetable functions, in the same 

 manner as minute parasites infest different parts of the animal struc- 

 ture. In addition to this, there must be in plants as well as in ani- 

 mals, a predisposition to receive the disease j for even epidemics 

 make a selection of their victims. The fungus did not attack all the 

 plants of the potato indiscriminately ; some varieties throughout the 

 infected districts having, comparatively speaking, escaped : a most 

 valuable fact for the consideration of the practical agriculturist. With 

 reference to the brown granules, which Mr. Goodsir believes to be or- 

 ganic, I confess I have been quite unable to satisfy myself regarding 



