634 



with the white Ureclo [Ureclo Candida), and it is ahtiost as common to 

 find this again covered with the Botrytis parasitica, although the lat- 

 ter is sometimes present on plants free from the Uredo. In this case 

 it is sufficiently evident that the vitality of the plant has been 

 diminished by the growth of the Uredo before the Botrytis is able to 

 fix itself upon it. Moreover, both these plants occiu' chiefly in the 

 autumn, when the leaves are verging toward decay. The Botrytis 

 effusa, which is a pest of spinach, and another species found on the 

 Chenopodium albidum, occur on yellowish, half-decayed spots, or 

 certainly spots in which the cellules of the leaf have lost their vital 

 turgidity. 



With this brief and imperfect outline of the habits of the parasitical 

 fungi, I arrive at the consideration of the question, — is the Botrytis 

 found on the potato leaf, a cause or, consequence of the disease ? If 

 wc were to take the anology of the Uredo, .^cidium and Puccinia, 

 we should be inclined to imagine that the sporules of this Botrytis 

 were absorbed by the roots, and carried with the sap to the parts in 

 which they are ultimately developed ; but this analogy does not ap- 

 pear to me to hold good, for reasons I shall presently detail. The 

 Uredines occur, as I have stated above, in otherwise healthy plants, 

 and provided they are not developed in very great abundance, the 

 functions of the plants are but little disturbed. The Mucorines 

 on the other hand seldom make their appearance except on decaying 

 vegetable or animal matter, and even when they do so, the plant or 

 the part of the plant on which they occur is usually if not invariably 

 in an unhealthy state ; the cells become more or less flaccid and the 

 colour is changed to yellow or brown ; they are indeed emphatically 

 the inhabitants of putridity. In the plants of potato affected with 

 this disease, I observed that the leaves became flaccid, either at their 

 edges, or presented flaccid and half-dried spots in the areolae of the 

 veins of the leaves, which quickly changed to brown, and ultimately 

 were crisped and curled, exactly such effects as I have seen to follow 

 the immersion of the roots in some poisonous metallic solutions. 

 The Botrytis was not to be found on all these spots ; some were 

 entirely free from it, while others were covered with the fungus. I 

 shall presently have to insist more strongly on this circumstance. 

 Where the Botrytis was found, on such spots it could not be traced 

 beyond the flaccid and dying or dead portions of parenchyma, and 

 gradually diminished in amount as it approached the margins of the 

 spots. I need not describe the characters or appearance of the Botry- 



