20 BOTANICAL GAZETTE [july 



form quite an even palisade and their bases converge toward a cen- 

 tral point below. This conveys the impression that they may have 

 arisen from a common central point or area. 



Spore-production follows very rapidly after the fusions. The 

 first spores formed are from the basal cells at the center of the fertile 

 layer in the region where the first fusions occurred. The wave of 

 spore-production proceeds from this center toward the borders of 

 the fertile layer and follows closely after the fusion wave. The 



9 



Fig. 6. — A mature aecidium of P. Eatoniae before the rupture of the epidermis: t, 

 lower epidermis; /, fertile layer; p 7 peridium. 



central basal cells continue to cut off spores and have usually pro- 

 duced a chain of 3 or 4 when the first spores are being produced 

 from the basal cells on the extreme lateral margins of the fertile 

 layer. The number of spores found in any one chain at this stage 

 is dependent on the position of the basal cell with reference to the 

 center of the fertile layer. The number decreases gradually from 

 3 or 4 at the center to one at the lateral margins. The surface of 

 the spore mass is thus dome-shaped, with the highest point of the 



