SpJiaena Morbosa. 205 



bark, and so affect it as to occasion an unnatural and excessive develop- 

 ment, a corky, irregular, warty growth, which finally bursts the outer cuticle, 

 and covers the infested branches with unsightly excrescences. To this 

 latter group belongs the Sphaeria morbosa. The fleshy growth which it 

 induces in the plum-tree, or at least that portion which is immediately 

 occupied by it, is called its stroma. This is, at first, a homogeneous mass, 

 presenting no definite character. By and by, it takes on a reddish colora- 

 tion, which finally deepens into black ; the surface becomes carbonaceous in 

 texture, and is studded all over with minute papillae. A section of the 

 stroma will then exhibit a woody centre with a carbonaceous rind. In this 

 rind are innumerable little rounded cavities, the upper walls of which con- 

 stitute the before-mentioned papillse : these are pierced by a minute hole, 

 through which the spores, or germinating processes, escape ; the whole cavity 

 and its walls being called a perithecmm. The spores are infinitesimally 

 minute, oblong bodies, contained, generally eight in number, in diaphanous 

 sacs, or envelopes, called asci, which develop from the ends of filaments, 

 which line, in a dense mass, the whole bottom and sides of the cavities. 

 These are not carbonaceous like the walls, but are of a gelatinous con- 

 sistency. Imagine an egg-shell, from the inner walls of which grows a 

 dense mass of soft bristles half an inch long, on the ends of which are 

 little whitish, sausage-shaped sacs, containing oval bodies lying diagonally 

 in the sacs, one applied to the other, sidewise, the bodies being variously 

 lined, and you have a tolerable idea of an immensely-magnified perithecium, 

 with its filaments, asci, and spores. 



That this structure we have just described should be a plant ; that this 

 hard, black, charcoal-like substance should be vegetable, — will seem strange 

 to those unfamiliar with the study of similar growths ; but it is vegetable, 

 and has so permanent a character as to constitute a species. It must be 

 allowed, however, that it is a matter of doubt, in mycology, how far the 

 same fungus may be affected by the plants upon which it fastens as to 

 change its habits and appearance. The older mycologists named the host 

 of parasitic fungi after the plants upon which they were found ; taking it 

 for granted that they were all distinct species if they had a different look. 

 Schweinitz, the great pioneer of the study in this country, has enumerated 

 a vast quantity of them in this way ; but, since later observations have 



