36o 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
A good demonstration of the presence of the fungus in the cedar can 
be made from free-hand sections. Fixed with Flemming's agent, the in- 
vaded tissues are blackened so that one sees a narrow ring consisting of 
phellogen and one or two adjacent rows of cells just below the cork, per- 
haps not over 5 to lo percent of the cortical zone (PL XXII, fig. 5, and 
text fig. 3). Bleached and stained with the triple stain, characteristic binu- 
cleated haustoria and hyphae become visible. It is undoubtedly the vigor- 
ous attack on the phellogen cells by the fungus that prevents the formation 
of the normal amount of cork. As soon as the spores have germinated in 
the spring a new cork cambium is developed in the cortex beneath the 
sorus, so that as the callus is formed all traces of the fungus disappear 
as last year's infected tissue is lifted up and sloughed off. This would 
leave pockets in the cortex beneath each old sorus devoid of fungus were 
it not for the reentrance of the parasite from the sides (C, C , fig. 3). The 
diagram represents this condition, Nov. 25, 191 7, in a small area from 
an infected limb twenty years old. Remains of the old telium {A) are 
still visible above the wound callus. There is a small region {!)) of phello- 
gen still free from the parasite. Now, if this infected area had been ex- 
amined in April of the preceding spring, the hyphae beneath the sorus 
would have been confined to the region of the cork cambium as shown 
in figure 4, Plate XXII. While, as stated, hyphae in such infections usually 
occupy only the two or three outermost layers of the living cortex (PI. 
XXII, fig. 5), yet one often finds the fungus halfway down to the phloem. 
The Origin of the Sorus 
The telial sorus may be said to originate in that region where the spore 
buds are formed. The sorus of G. clavipes would be subcuticular in a 
broad sense because the subterminal cells in the plectenchymatous primor- 
dium are formed in the cuticularized layer of the host, which would be 
somewhere between the cuticle and the lumen of the epidermal cell beneath. 
The Telium in the Leaf 
In view of the very superficial attack on the leaf and young stem tissues 
by the fungus, which appears to get much of its nourishment from the 
epidermis, it does not seem strange that the sorus primordium should be 
found originating in the cuticularized layer. The point at which a sorus 
will develop is usually marked by a massing of hyphae, so that the cuticle 
is widely separated from the underlying cells (fig. 4, D). As the primor- 
dium enlarges and spores are formed, the cuticle, carrying some portion 
of the cuticularized layer which has become more or less disorganized, 
breaks away along a line and folds back so that the nature of the sorus 
can be determined very readily. A small sorus is shown at E, figure i, 
where the mycelium is deep-seated. The large cells {E) at the base of 
the sorus are the supporting cells of the stomata on either side. Another 
