Dodge: The Genus Gymnosporangium 185 



parenchyma cells in the region between the pits are larger than 

 are those beneath the depressions. This might bring about the 

 formation of the pits. Pits are not formed in galls caused by G. 

 globosum, and in most species of this genus the host cells with 

 which the hyphae are associated are usually hypertrophied. In 

 some cases pits are formed in galls before there is any massing 

 of the mycelium in preparation for the formation of a sorus, and 

 I have not noticed any great destruction or crushing of paren- 

 chyma cells of the host in early stages of sorus formation as 

 stated by Reed and Crabill. 



Hyphae were quite commonly present in the parenchyma of all 

 parts of the galls fixed November 30, but they were in much 

 greater abundance in the region beneath the depressions. In the 

 least matured specimens the hyphae had just begun to push in 

 between the outer and smaller parenchyma cells directly beneath 

 the central part of a depression. Later stages show that these 

 hyphae begin to branch (PI. 9, Fig. 1) and become fairly definitely 

 directed. The cells are slightly larger than the cells of the vege- 

 tative hyphae. Their nuclei are very conspicuous, both visible, 

 lying on the long axis of the cell. Although the ends of the 

 branches do not appear to be pushing strongly against the cork 

 layer above, a small space now exists between the cork and the 

 parenchyma of the host. As these hyphae branch and new cells 

 are added, a quite definite loose palisade of radially directed 

 hyphae is formed, the cells of which are somewhat longer than 

 broad. The hyphal mass becomes more compact so that a pseudo- 

 parenchyma is formed with cells more or less rectangular or poly- 

 hedral in shape. The two nuclei now occupy various positions in 

 the cells (PI. 9, Figs. 2, 3). The upper cells grow against the 

 cork layers and become somewhat flattened but they are usually 

 slightly longer than the cells beneath. They soon begin to swell 

 or elongate, their cytoplasm becomes more vacuolate and the 

 nuclei take the safranin stain, while the nuclei of all the cells 

 below take the gentian violet. The buffer cells finally become two 

 or three times their original length and contain only a thin watery 

 substance that is faintly colored with orange G. Their walls be- 

 come thinner and thinner and finally disappear altogether. The 



