M. C. COOKE ON BLACK MOULDS. 253 



chains. There arc points of affinity in which these two genera 

 approach so closely, as for instance in Dendryphium laxum, and Hel- 

 minthosporum rhopaloides, that it is difficult to indicate any manifest 

 difference except in the mode of spore production. It may generally 

 be predicated that the threads of Helminthosporium are unbranched, 

 or nearly so, and that the threads in Dendryphium are more or less 

 branched in the upper portion. This may seem, at first, to be a 

 slight difference, but it gives a peculiar character to each, which 

 cannot but impress itself forcibly upon the mind whenever the two 

 are compared under the microscope. In the general features of 

 these two genera they are allied to Helminthosporium, but in spore 

 production they link that genus to Cladosporinm. If it were per- 

 mitted me to pause and speculate, it would form a good topic for 

 reflection how, in each genus, one species had tendencies in one 

 direction and others in another, how form approximated to form, 

 and how here, as well as in every other portion of inexhaustible 

 Nature we encounter continuous chains of being, linked and bound 

 one to the other, touching everywhere, and, amidst endless variety, 

 united into one harmonious whole. 



A very natural group of Black Moulds are those of which Clados- 

 porinm, may be taken as the type. These moulds differ from the 

 preceding in one important feature, the flocci are not rigid and opaque 

 or semi-opaque, there is no evident external coating, and when dry 

 the cells collapse freely, which indicates a much more delicate cell- 

 wall than prevails in the Helminthosporium type. There are four 

 genera, to which I would direct your attention for a few moments, in 

 this group. First of all there are those which have been classed 

 with Helminthosporium as aberrant forms, such as the one found by 

 Messrs. Berkeley and Broome on leaves of Lychnis, and by them 

 called Helminthosporium echiuulalum. Not long since my friend Mr. 

 Phillips, of Shrewsbury, sent me a mould on the leaves of Star of 

 Bethlehem, and this I at first referred to Berkeley's species, but on a 

 subsequent and more minute examination I find it to be identical 

 with a specimen I possess from the late Dr. Klotsch, marked Hete- 

 rosporium ornithogali, Kl. MSS. The threads are long, flexuous, 

 with thin walls, pale-brown, much divided, sometimes branched, with 

 spores of most irregular size and form, some are elliptical and simple, 

 others uniseptate and longer, others are again much more elongated 

 and cylindrical, with two, three, or more septa, so that the longest 

 are about five times the length of the shortest, and externally faintly 



