72 M. C. COOKE ON NETTLE STEMS AND THEIR MICRO-FUNGI. 



Altliongli this and some other species here enumerated have only- 

 been detected on nettle stems, it does not follow by any means that 

 they are confined to such a habitat, or that some other allied species 

 found on other herbaceous plants may not also occur on nettle stems. 

 At present our knowledge of the distribution of these minute forms 

 is too limited for generalizations of this kind. 



Externally, and to the naked eye, resembling a very thin patch 

 of the Torvla, another, and widely different fungus, may be found 

 in a similar location. In this instance the coating is so thin that 

 it only gives a greyish appearance to the stems, the black threads 

 being sprinkled about in patches two or three inches in length. 

 When held up between the eye and the light, and examined by 

 a pocket lens, the twig appears velvety with erect black hairs, an 

 appearance never presented by the dense growth of the pulverulent 

 Torula. This is the general appearance of two species of Den- 

 dryphium^ a genus of black moulds distinguished by the jointed 

 threads being branched in the upper portion, bearing at their apices 

 septate spores, which are often attached end to end in a series. In 

 one species^ the fertile branches are radiating, or form a dense head, 

 and the septate spores are variable, with the joints quadrate. This 

 is called Dendryi^hium comosvm. In the other species, Dendryphkim 

 cuitiim, the branches are shorter, and forked ; the spores are curved, 

 with from three to seven septa, constricted at the joints. The 

 shorter forked ramuli, and the much constricted articulations of the 

 spores, are characteristic of this species. Both of them are found 

 on old nettle stems, as also a third species — Dendryphium griseum 

 — which is very different in its appearance to the naked eye. In 

 this latter the stems are covered in patches of some extent, with a 

 bluish-grey bloom, something like the bloom of a ripe plum. The 

 threads are but slightly branched, and the spores are cylindrical, 

 with a little point at each end, and arranged in chains ; they are at 

 length uniseptate, and colourless. There is something so very dif- 

 ferent in the appearance of this species and its colour, that at first 

 it would scarcely be recognized as belonging to the same genus as 

 the two preceding. It is often very common amongst the debris 

 of an old bed of nettles. 



Another black mould may be named in this association, which, 

 though perhaps much less common, is even more beautiful (fig. 3). 

 It is Arthrohotryinn atrum. In this instance the common stem 

 is composed of jointed threads, which are attached together 



