OF PI, ANTS. 293 



deep ploughing of* the furrow in iron-shot soils, may contri- 

 bute to the diffusion of Wight or rust. 



423. 



The innumerable kinds of Coniomyci which are connect- 

 ed with blight or rust, are undoubtedly individual forms ; 

 but they seem to owe their origin to a peculiar transforma- 

 tion of the spherical and vesicular bodies, which the genera- 

 tive sap contains. We hence see them appearing in abun- 

 dance upon healthy leaves, in which we observe either a su- 

 perfluity of juice, or a perspiration of the generative sap. 

 This is obviously the case with the Uredo Candida, which ap- 

 pears in abundance upon the Thlasp'i bursa, and is coveretl 

 with an inflated epidermis. The same thing is distinctly per- 

 ceived in the Uredo tremellosa and cincia of Strauss, the pro- 

 duction of which is commonly attended by the perspiration of 

 a fluid having the appearance of a jelly. And the Neinaspo- 

 ra, of which a great many kinds appear upon the branches of 

 the Poplar, shews, beyond all doubt, that it owes its origin to 

 the generative mucilage. 



Again, we frequently see the degenerating j uices of the leaves 

 becoming hard and producing shapeless masses of a blackish 

 colour, which are called xyloma, and have the appearance of 

 new shoots that have died. But if, by the influence of the 

 original vital powers, a new activity is awakened in the juice 

 which had been thus entirely changed or dead, the primitive 

 forms again appear in their simplest state. They appear as 

 spheres or vesicles, as in Eurotium, Camptosporium, Spodo- 

 phlciun (Tab. V. Fig. 5, 7.), Podismay Phacidhwi, and other 

 Fungi ; among which, however, there are some that seem 

 but slightly to injure the health of the leaves, because they 

 seem to be formed from the perspired sap upon the ejViderrais 

 only, as in the instance of Phijllerium. It often happens, 

 however, that the epidermis of the leaf is torn at the snxm^ 

 time, and surrounds, in a definite and peculiar liirm, a crowd 

 of Coniomyci, which have been generated in the sap, (/E<7- 

 dium, Rostelia.) 



