C. H. PECK OX THE *' BLACK KNOT. bO 



because in one or two points vre cannot quite agree with the in- 

 ferences and conchisions of former investigators. 



If the smaller branches of a cherry tree that is suffering from 

 an attack of black knot be carefully examined in Xovember, some 

 of them will be found to be slightly swollen for a little distance 

 immediately below the excrescences. The cuticle of the bark will be 

 cracked open here and there, revealing the soft tissues of the inner 

 bark. If a minute portion of this inner bark be examined by the aid 

 of the microscope, slender jointed filaments or threads may be seen, 

 that have insinuated themselves among the bark cells. These 

 threads are the primary vegetating condition of the fungus, and 

 are known to botanists as wycelium. During the winter the en- 

 largement of the branch remains nearly or quite stationary, but 

 with the advent of spring and the renewal of vegetable activity, 

 the tumours increase in size, the chinks in the bark become wider 

 and more numerous, and by the end of May small, dark, green 

 stains are visible in the crevices of the bark. These greenish 

 patches gradually increase in size until in some instances they com- 

 pletely cover the whole surface of the excrescence with a soft, 

 velvet-like coat. Such specimens were once sent to me from the 

 west, where they had been pronounced by a scientific journal to be 

 a new species of black knot. A microscopic examination of this 

 greenish coating reveals the fact that it is composed of innumerable 

 upright, jointed, flexuous threads or flocci, which bear upon their 

 summit oval or oblong spore- like bodies, at first simple, but soon 

 becoming one or more septate. This is the first external develop- 

 ment of the fungus, and in the systematic classification adopted by 

 botanists it belongs to the genus Cladosporium. This genus, 

 however, we apprehend is destined to be overthrown, its species 

 being only an early form of development of species of Sphceria. 

 Indeed those celebrated European mycologists, Tulasne and Cooke, 

 already deem the very common Cladosporium herharum to be only 

 a condition of Sphceria herbarum. And here we have another 

 quite clear case of a similar dimorphism, for I never yet have seen 

 a young black knot excrescence of the cherry tree in spring on 

 which I could not detect the Cladosporium. In a few weeks this 

 Cladosporium growth is succeeded by numerous minute, black, 

 globular bodies, scarcely as large as the head of a small pin. These 

 usually cover the whole surface of the excrescence, and are often 

 BO closely crowded together that they partially lose their globose 



