1914] 



FROMME—AECIDIUM CUP 



21 





dome 



It is convex in vertical section, while the sur- 



face of the fertile layer is concave. 



mass of spores forms 

 ) the epidermis, 

 at a uniform rate aci 



dome 



mass is elevated or pushed toward the epidermis 



The 



Fig. 7. — A mature aecidium of P. Hydrocotyles before the rupture of the epi- 



dermis: c, lower epidermis 



thin-walled, empty cells of the pseudoparenchyma apparently offer 

 but little resistance. They are crushed and pushed upward or to 

 one side, and either disappear entirely or remain as a thin layer of 

 material without cellular structure. Meanwhile the leaf epidermis 

 has been pushed up as an arch over the developing spore mass, as 

 the result of the pressure, and when the pseudoparenchyma has 



