1914] FROMME—AECIDIUM CUP 23 



hand border. The extreme outer border chains have as yet pro- 

 duced no peridial cells, and it is evident that the 4 peridial cells 

 shown in the figure could not have been produced by them. The 

 figure shows, further, that not all of the interior spore chains pro- 

 duce peridial cells, since the apices of some of these do not reach 

 to the outer surface of the spore mass. A more complete peridium 

 at a later stage is shown in text fig. 8, b. Eleven peridial cells 

 appear in this section; 7 of these have apparently been borne on 

 interior chains, although their connection with any one chain can- 

 not be determined with certainty. The long axes of these cells are 

 perpendicular to the epidermis and parallel to the axis of growth of 

 the interior chains. The other 4 peridial cells, 3 on the left and 1 

 on the right, are evidently borne in the peripheral chains. It is also 

 evident from this figure that not all of the interior chains have pro- 

 duced peridial cells, since there are 20 interior chains and but 7 



peridial cells of interior origin. 



While the peridial cell is forming, its connection with the spore 

 chain on which it is borne is evident (text fig. 8) , but with its enlarge- 

 ment at maturity and the changes in its position brought about by 

 the continued elevation of the spore mass, this connection is made 

 difficult or impossible to determine. 



Not all of the peridium is formed from sterilized apical aecidio- 

 spores; its lateral walls are made up of the entire peripheral spore 

 chains (text fig. 8, b). The cells of these chains are distinguishable 

 as peridial cells when they have become the third or fourth cell from 

 the base of the chain. The cells that make up the lateral walls of 

 the peridium are differentiable from those that form the central 

 arch in that they are modified aecidiospore initial cells rather than 

 aecidiospores. They do not, except perhaps in rare cases, produce 

 intercalary cells. Both the cytokinesis and karyokinesis of these 

 cells are apparently inhibited by the same agent that produces the 



metamorphosis of the cell. 



The production of peridial cells proceeds from the central point 

 of the apical surface of the spore mass outward in all directions 

 until a complete layer is formed over the entire apical and lateral 

 surfaces of the spore mass. The peridium of this type of aecidium 

 is normally but one cell in thickness. It is interesting to note, 



