206 PROCEEDINGS OF THE AMERICAN ACADEMY 



occur shows a cavity in the leaf tissue below each swelling. This 

 cavity arises from a separation of the epidermis and the leaf paren- 

 chyma at their plane of union. The epidermis bows up, producing the 

 appearance of the swellings previously described, and the leaf paren- 

 chyma, instead of following the epidermis in its upward folding, tears 

 away from it, and remains unaltered in position, or by shrivelling 

 sliglitly sinks downward away from the epidermis, and thus increases 

 the intervening space. The cavity, since it has considerable lateral 

 extension compared with its depth, is quite shallow. The leaf paren- 

 chyma forming its floor is penetrated in all directions by the mycelium 

 of the fungus ; this mycelium on approaching the lower surface of the 

 cavity gives rise to a great number of upward-growing filaments, which 

 project into the cavity itself and form a sort of hymenium. On the 

 free ends of many of these fdaments the yellowish uredospores are 

 born. These spores, after ripening, generally escape through the 

 crater-like opening in the epidermis above ; but often before they have 

 completely disappeared the dark brown glistening heads of the teleu- 

 tosporic stage may be seen emerging from the lower surface of the 

 cavity, and, in the older leaves, filling completely the crater-like open- 

 ings, which soon become much larger by the crumbling away of the 

 surrounding dried epidermis. Several of these openings, by contin- 

 ued increase in size, may eventually run together, and thus compara- 

 tively large spaces on the leaflet may be covered with teleutosporic 

 heads. 



Although the heads usually occupy old depressions made by the 

 uredospores, they occasionally form depressions of their own. Such 

 a grou[> may be seen in Figure 1. Here several individuals are still 

 under the epidermis, while one has burst through and is projecting 

 from the upper surface of the leaflet. The under surface presents a 

 broad depression, from which, unfortunately, most of the heads were 

 removed in the process of softening and cutting. This lower cluster 

 presented all the appearances of one developed in a depression pre- 

 viously formed by the uredospores, and it is probable that the heads 

 above are simply an outgrowth from the same stock of mycelium as 

 that which gave rise to the larger cluster below. Thus far, all the 

 heads found on the leaflets have been easily referable to their re- 

 spective depressions, the instance shown in Figure 1 being the most 

 anomalous yet observed. Should the explanation as applied in this 

 instance prove generally true, it may be stated that the heads on the 

 leaflets develop at a later period, but in the same depressions as tho 

 uredospores. 



