July, 1922] DODGE STUDIES IN THE GENUS GYMNOSPORANGIUM 
365 
covery of other rusts outside this genus whose teliospores arise from sub- 
terminal cells. 
Summary 
The sporophytic mycelium of Gymno sporangium ' clavipes on Juniperus 
virginiana in the periods of exploration and attack is found in the cuticu- 
larized layer of the epidermal cells of the leaves and young stems. As 
the season advances the hyphae penetrate into the mesophyll. In cork- 
covered stems the parasite is generally confined to the two or three outer- 
most layers of cells of the living cortex, although hyphae are sometimes 
found much nearer the phloem. Characteristic binucleated haustoria occur 
in the cells of the epidermis and mesophyll. 
The first sori always appear either directly on the leaves or, more 
commonly, on the stems at the margins of the decurrent leaf bases or 
in the leaf axils. In later years, as cork is laid down on the stem, the 
sori are formed and break through in the ordinary manner. 
Sori on leaves and young stems are subcuticular to the extent that 
they arise in the cuticularized layer of the epidermal cells. 
The teliospore buds grow out from the subterminal cells of the basal 
primordium, the terminal cells having become disorganized and swollen, 
functioning as buffer cells. 
Fruit Disease Investigations, . , 
Bureau of Plant Industry 
EXPLANATION OF PLATE XXII 
Gymnosporangium clavipes 
Fig. i. Longitudinal section of a part of a leaf at the edge of the vein. The myce- 
lium is found principally in the upper epidermis from a to e. At h, c, and d, hyphae have 
invaded the mesophyll as shown by the darker regions. 
Fig. 2. Section of infected branch of red cedar showing three regions containing 
mycelium. 
Fig. 3. More highly magnified view of a portion of a similar section. The dark 
area between the leaf bases shows the limits of penetration. 
Fig. 4. Section of a sorus on a larger limb; the mycelium beneath is confined to 
the region of the cork cambium. A fragment of the ruptured cork is seen at the left. 
Fig. 5. Section from an infected area between two sori; the mycelium is likewise 
very superficial. 
Fig. 6. Section of an infected stem similar to the one shown in figure 2, but made 
January 19th, the following winter. The old infected tissue has been cut off by wound 
callus (center above), and hyphae have grown in from the sides, attacking the cork cam- 
bium present only between the two leaf bases. 
Fig. 7. Cross section at the edge of an infected leaf. The dark region indicates 
where the fungus is present. Cross sections of the hyphae are best shown in the cuticular 
layer. 
Fig. 8. Surface view of a fragment of the cuticle with attached cuticularized layer 
raised above the sorus. Two kinds of markings: the outlines of the epidermal cells, 
and the corrosion pockets left by the hyphae or buffer cells of the sorus. 
