Oct. 1, 1925 
Telidl Sorus in the Pine Rust 
643 
THE PERIDIAL BUFFER TISSUE 
There is very little intermingling or intertwining of hyphae as a 
preliminary to the formation of the telial sorus. The hyphal com¬ 
plex below is usually no denser than it is in other parts of the leaf. 
The hyphae push otit between the mesophyll cells ana widen suddenly 
just before reaching the ends of the large lobes of these cells. Since 
the hyphal branches grow straight out against the hypodermal tissue 
in a solid rank, the epidermis and underlying tissue are stretched and 
pushed outward. Each chain in the palisade of fungus tissue is com¬ 
posed of four or five uninucleated cells (fig. 1, A). The buffer effect 
is considerably increased as the terminal cells lose their granular 
cytoplasmic contents and elongate (fig. 1, C, a). The propriety of 
calling the layer of terminal cells which persists a peridium is dis¬ 
cussed later. 
CELL FUSIONS 
Up to this time there is nothing in the appearance of the cells of 
the primordium to indicate exactly where cell fusions are to occur. 
Soon after the epidermis is ruptured, however, the sorus takes on 
quite a different appearance. Cell fusions which are readily dis¬ 
tinguished are seen along a line beneath the point of rupture (fig. 1, 
B to D). The fusing cells are the second or third cells from the outer 
ends of the chains, and are therefore intercalary. The writer has not 
seen fusions between subterminal cells, but this may sometimes 
occur. Neither are the fusions all on the same level (fig. 1, E). 
There are more frequently two sterile cells in the chains above the 
fusing cells (fig. 1, B and D). The conjugations are more readily 
seen in sections that show the gaps between the lobes of the mesophyll 
cells. The adjacent walls of the fusing cells quickly disappear, and 
the two nuclei come closer together (fig. 1, C). The cell thus formed 
enlarges but its cytoplasm becomes only slightly less vacuolate. 
At the same time the buffer cells immediately above collapse. The 
terminal cells of the chains, however, retain their form and persist 
indefinitely as a sort of peridium, or until cast off with fragments of 
the ruptured leaf tissue above (pi. 1, C). 
CATENULATE SPORES 
The fusion cell quickly divides, and the upper daughter cell 
develops a very dense cytoplasm so that it takes the stains readily. 
The fusion cell still remains vacuolate. As the sorus ages and in¬ 
creases in size, the buffer cells at the margin elongate correspondingly. 
The digestive effect which the newly formed spore cells have on this 
tissue is strikingly demonstrated by the way the fertile layer broadens 
laterally (pi. 2, A, and fig. 1, E). Although the sub terminal cells in 
the chains are completely destroyed, the terminal cells, at least the 
outer ends of them, persist, as noted above (pi. 1, C). From this 
time on, the number of binucleated spore cells cut off in the chain 
above each fusion cell increases. At the margin, nuclear fusions 
may occur in the second or third spore of the chain (fig. 1, E); while 
at the center, there may exist three or four binucleated potential 
spore cells, above which there are one or two spores, considerably 
elongated and rich in cytoplasm, but still binucleated (fig. 1, K). 
Above these the spores are much longer and uninucleated (fig 1, J 
