July, 1922] DODGE — STUDIES IN THE GENUS GYMNOSPORANGIUM 
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young stem. After the leaves are shed, the fungus, closing the gaps, will be 
found in the cortex around the entire circumference of every section. The 
diagrams bring out very strikingly the fact that the mycelium never gets 
very near the conducting systems of the host. Wornle {I.e.) states that 
he found mycelium of G. clavipes in the bast. He was apparently mistaken 
in this regard, as I have seldom if ever found hyphae approaching phloem 
very closely. 
The Mycelium in Trunk Infections 
The fungus at first advances longitudinally in the stem one to three 
centimeters each year but circles it very slowly, sometimes taking several 
years in the process. In many cases of trunk infection the mycelium is 
always confined to a small region and never completely girdles the tree. 
Where the stem is attacked in a rapidly growing region, such as at the 
end of the main axis or at the tip of a well exposed branch, the fungus is 
outstripped by the host, the infection being recognizable in later years 
by the slightly fusiform swelling. If infection takes place on a slowly 
growing side branch, the parasite grows upward with the host, penetrating 
new branches, frequently causing, as a consequence, distortions like small 
witches' brooms. 
The main trunk of the cedar may also become infected, even after 
many layers of cork have been laid down, as a result of the downward 
growth of hyphae from an infected branch. Such secondary infections may 
account for the types of injury characterized by black patches a few inches 
in diameter on trunks of large trees, showing how little damage may be 
caused by this species during the fifty or one hundred years which have 
passed since infection occurred. 
Fig. 3. Diagram representing a small portion of the cortex, Nov. 25, 191 7, of an 
infected cedar limb twenty years old, showing the manner in which the wound callus cuts 
off the old sorus and adjacent infected tissue of the preceding spring. A, remains of telio- 
spore stalks. B, wound callus cork. C, cork cambium and one or two layers on either 
side among the cells of which hyphae have invaded from the margins. D, uninfected 
gap of cork cambium which will soon be invaded. E, uninfected cortex, which extends 
much farther down. 
