

1914] 



FROMME—AECIDIUM CUP 



19 



ably located for spore-production than those that lie more deeply 



in the tissue. 



The elongation of the fusion cell formed at 



the 



surface of the tissue is unimpeded except for the slight resistance 

 offered by the empty, thin-walled cells of the pseudoparenchyma, 

 while the fusion cell formed below must force its way between the 

 closely packed gametes and fusion cells above. Sometimes they 

 are able to do so and function as basal cells, but many were found 

 that were apparently inhibited from so functioning by the resistance 

 of the overlying cells. 



Fig. 5. — A mature aecidium of Ur. Caladii before the rupture of the epidermis: 

 e, lower epidermis; /, fertile layer; p y peridium. 



The fertile layer is deeply concave in P. Claytoniata and P. 

 Violae, and extends about halfway up the lateral surfaces of the 

 cup. The basal cells are more or less uneven in height, and the 

 surface of the layer in outline has an irregular, broken appearance. 

 The fertile layers of Ur. Caladii (text fig. 5) and of P. Eatoniae 

 (text fig. 6) are especially broad and only slightly concave. The 

 fertile layers of P. Hydrocotyles (text fig. 7) and of P. angustata are 

 narrow and only slightly concave. The production of spore chains 

 is confined to the basal surface of the cup and does not occur on the 

 lateral surfaces. The basal cells of P. Hydrocotyles (text fig. 7) 



