OF ARTS AND SCIENCES. 209 



The cell contents in the matured state seem to have disappeared com- 

 pletely, and all that remains is a delicate, thin-walled, almost trans- 

 parent cyst, formed by the old cell wall. When the fungus has been 

 allowed to ripen fully on the leaflet, the natural method for the detach- 

 ment of the spore-mass seems to be by rupturing the cyst region. 

 After the cysts have thus broken close to the stem, their jagged edges 

 stand out as a sort of frill surrounding the spore-mass (Fig. 9). It is 

 probably this stalkless stage of the American H. glandulceformis which 

 has been considered identical with the Indian R. sessilis, Berk. When 

 many spore-masses become thus disconnected with their stalks, the 

 irregular margins of their frills may mat together and form a continu- 

 ous layer. In one instance, a mat composed of perhaps a hundred 

 such spore-masses was lifted on the point of a knife from the surface 

 of the leaflet. It held its form well, and could be turned on a slide, 

 so as to expose, first its upper, then its lower surface, without tearing 

 the heads apart. 



The stalk presents more difficulties in the way of its study than 

 either of the other two regions. In the dried specimens it was so 

 much shrivelled that all attempts to get good sections showing its 

 relation to the cyst-cells failed. Moreover, the density of the embed- 

 ding material was such that it intensified the shrivelling (Fig. 8). By 

 maceration and surface study of specimens swollen in a warm solution 

 of potassic hydrate fair results were obtained. 



The stalk is undoi;btedly compound, since by pressure it may be 

 split into a number of longitudinal filaments, the stalk-cells, extending 

 its whole length. From the exterior each of these cells may be seen 

 to abut against a cyst-cell (Fig. 10), and, since but one stalk-cell has 

 been seen to adhere to a cyst-cell in all successfully macerated mate- 

 rial (Fig. 11), it is highly probable that each cyst-cell rests upon a 

 stalk-cell in much the same way that the cells of the spore-mass rest 

 upon those of the cyst region. 



The cells of the stalk are long, and by mutual pressure more or less 

 angular ; at their tops they expand slightly in order to clasp the cyst- 

 cells, and below they unite with the mycelium in the leaf tissue. 

 They have walls as thin as those of the cyst-cells, but, unlike these, 

 they appear to possess slightly granular contents. 



Since each stalk-cell supports a cyst-cell, and this in its turn sup- 

 ports a spore-cell, it becomes possible to consider the whole head as 

 composed of a bundle of fused aerial hyphpe, bearing spores on their 

 summits. The hyphie consist of two parts, a simple stem portion and 

 a cyst-cell. Each hypha carries on its cyst-cell a spore, which, if the 



VOL. XXII. (n. S. XIV.) 14 



