1914] FROMME—AECIDIUM CUP II 



ma 



them. Their cvtoolasm 



the nucleoles especially large and prominent. They are apparently 

 richly nourished at the expense of the cells of the underlying hyphae 

 and vegetative mycelium. These richly nourished cells form a 

 tissue, 2 or 3 cells in depth, that lines the inner basal surface 

 of the young aecidium cup and extends for some distance upward 

 on its lateral surfaces. 



A comparison with the caeoma type of aecidium naturally sug- 

 gests that these richly nourished cells are the gametes, and, as a 

 matter of fact, practically all of the cells of this cup-shaped tissue 

 may later fuse in pairs. Even though the fusion of all of them is 

 not ultimately accomplished, the fusing pairs are distributed 

 throughout the tissue and, before the fusions, those which are to 

 fuse cannot be differentiated from the others. 



These gametes of the aecidium cups of P. Claytoniata are quite 

 comparable to the gametes of the caeomas. The aecidium of the 

 caeomas is broad and shallow, and the gametes are produced in a 

 single continuous layer beneath the leaf epidermis from which they 

 are separated by a single layer of sterile cells only. They are the 

 penultimate cells of the gametophoric hyphae. The aecidium of 

 P. Claytoniata is spherical in shape and is deep-seated in the tissue 

 of the host. The gametes form a tissue, 3 or 4 cell layers in depth, 

 that lines the basal surface of the spherical mass. Above the 

 gametes is found a tissue of sterile cells that has resulted from the 

 disintegration of the upper two-thirds of the gametophoric hyphae. 

 In the cup both the gametes and sterile cells form a tissue, while in 

 the caeoma they form but a single layer. The sterile cells of the 

 pseudoparenchyma and the "buffer" cells of the caeoma seem to 

 be of similar origin and bear the same relation to the respective 

 gametes above which they are borne. In both cases they are pos- 

 sibly potential gametes which have become sterile. If the sterile 

 cells of the cup and the "buffer" cells of the caeoma are in reality 

 homologous, Blackman's conception, that the latter are morpho- 

 logically trichogynes, would have to be extended to include a 

 pericellular type of trichogyne. It may be noted in passing that 

 Olive (22) contends that the "buffer" cells are sometimes wanting 



