192 



Mycologia 



Fig. 2. Older stage. About one third of the primordium is shown here. 

 Further extension is being made at the left. Degenerating terminal cells are 

 shown at the center, and spore buds are pushing into or between buffer cells 

 at the right. The nuclei are just dividing in one bud. The walls of the over- 

 lying cork cells at the right are being pushed in. 



Fig. 3. At the center of another young sorus. Shows that some terminal 

 cells disintegrate more quickly than others. The position of the nuclei in a 

 young bud just prior to division can be seen at the left. The cork cells are 

 very irregular and are somewhat distorted by pressure. 



Fig. 4. A portion of an older sorus at the stage when the papilla is qtiite 

 noticeable. Two cork cells (at the left) are completely broken up and spores 

 are nearly mature. Two or three spores or spore buds arise from each basal 

 cell. No traces of buffer cells can be seen. At the right of the cells bearing 

 two-celled spores there are six or seven basal cells that bear spore buds in 

 which the stalk cell of each has just been cut off. There are one or two buds 

 having three cells. The next region shows two-nucleated buds and other buds 

 just forming. Traces of buffer cell walls are now visible as mere lines. At 

 the right in the figure the degenerating terminal cells are very distinct. This 

 figure shows the conditions near the border of the blister-like swelling. Note 

 the abrupt transition here, practically all stages in spore formation from those 

 in which the terminal cells still possess nuclei to the stages where two-celled 

 spores are completed. 



Plate 10 



Fig. 5, Gymno sporangium globosum. The central portion of a young 

 primordium. Terminal cells have elongated slightly but have not begun to 

 degenerate. The nuclei are somewhat larger than are those in the primordium 

 of G. macropus. 



Fig. 6, Gyymnosporangium clavariaeforme. The region at the margin of a 

 young sorus at the center of which spores are just beginning to form. The 

 cells from which the spore buds arise are plainly at a lower level than the 

 terminal cells at the left. The host cells contain masses of some deeply stain- 

 ing substance showing degeneration, but their nuclei appear to be quite normal. 

 An haustorium is shown in one cell. 



Fig. 7, Gymno sporangium clavariaeforme . Region at the center of a 

 younger sorus. In one cell a bud is just forming. Nuclear division is occur- 

 ring in the buds from three adjacent subterminal cells, one of which also 

 has a bent two-nucleated lateral bud. 



Fig. 8, Gymnosporangium nidus-avis. Near the margin of a large sorus 

 on a naturally infected plant. Mature spores were present at the center and 

 the cork had just been ruptured. There were about fifteen rows of flattened 

 thick-walled cork cells above the region shown in the figure. 



The nuclei of the terminal cells are small, and degeneration is not pre- 

 ceded by such an amount of elongation as occurs in the other species. A 

 lateral bud and an internal spore bud are shown at the right. The nuclei of 

 the cells of the pseudoparenchyma are rather large. 



Plate i i 



Figs. 9 and 10, Gymnosporangium globosum. The upper figure shows the 

 conditions from the margin of a sorus inward. The lower figure is drawn 



