DODGE: STUDIES IN THE GENUS GYMNOSPORANGIUM 139 



not occurred (Text-fig. 5, D). Remnants of buffer-cell walls were 

 now difiicult to find. A mature spore is shown in Text-figure 5, E. 



The mycelium of G. fraternum penetrates through the leaf in every 

 direction. The mesophyll cells are usually somewhat enlarged and 

 are packed rather closely together with small intercellular spaces. 

 Haustoria are quite abundant in such cells. The cells surrounding 

 the vein are especially affected. They appear to be filled with minute 

 granules and as many as eight or ten haustoria can be found in a 

 single cell, the more common number being two to four. A complete 

 ring of these large cells is formed. This is due to an increase in 

 number as well as their larger size. This, taken in connection with 

 the increase in the mesophyll tissue, gives the leaf a slightly thicker 

 and more compact appearance. The mycelium does not invade the 



Fig. 5. a, pseudoparenchyma with buffer cells; b, 2-nucleated stage of the 

 young teleutospore; c, 4-nucleated stage; d, 6-nucleated stage with cross walls; e, 

 small spore after nuclear fusion. 



vascular tissue even to the extent of penetrating the phloem of the 

 stem. Both G. transformans and G. fraternum are capable of producing 

 sori two or three years in succession, the latter may produce a. sorus 

 even after the leaf has apparently died. While haustoria are more 

 numerous and attack the individual cells more vigorously in the case 

 of the latter species, G. transformans seems in some way to be more 

 destructive, as infected leaves more frequently die after maturity of 

 the first sorus. Of the two species, G. fraternum is clearly the more 

 nearly related to G. biseptatum, both from the nature of their teleuto- 

 spores and the similarity of the aecidia in the two species. If the 

 mycelium of G. fraternum is ever able to push in beyond the large cells 

 surrounding a vein and get into the central cylinder of the stem, 

 therefore nearer the cambium, we should look for a stimulus such as 



