MICHIGAN ACADEMY OP SCIENCE. 55 



A CANKER OF THE YELLOW BIRCH AND A NECTRIA ASSOCIATED WITH IT. 



Jas. B. Pollock. 



In January, 1905, Miss Harriet W. Thomson sent to the botanical laboratory at the Uni- 

 versity of Michigan some branches and twigs of a yellow birch that were badly affected by 

 a form of canker. The material was collected near Port Sanilac, Michigan, and the cause 

 of the trouble, whatever it is, has been at work for a number of years, as shown by the 

 growth of the larger branches since they were first attacked. The collector of the mate- 

 rial however can remember when the birches of this same place were completely free from 

 any such trouble, so that it may have been of recent origin in that region. 



The largest branches sent in were about 5 cm. normal diameter, but in the enlarged 

 parts adjacent to the dead areas the diameter of some was 7 cm. or more. On the young 

 branches it was easily seen that the disease started aroimd the base of dead twigs in a con- 

 siderable number of cases. The cause of the trouble does not spread rapidly in the tissues 

 of the wood, since cankered spots separated not more than 5 cm. have not coalesced after 

 several years development. Often the dead areas extend farther in the direction of the 

 circumference of the stem than in the direction of its long axis. A branch may be almost 

 girdled, and yet the dead part has only a slight extent vertically. Thus, one spot meas- 

 ured 14 cm. in the direction around the branch, over the swollen parts adjacent to the dead 

 area of wood, while above and below the dead area the edges of the callus with which the 

 tree tries to cover over the wound were only 1 cm. apart at the nearest point, and 2.5 cm. 

 at the widest part. Apparently the cause of the trouble acts as a stimulus to growth of 

 the living parts adjacent to the killed portion, and this leads to the disfiguring knots or 

 swellings at the border of the dead areas. Over some of the cankered spots on the small 

 branches the outer layers of the bark are still continuous, though the hypertrophy about 

 the border is well marked, leaving a depressed center, which is probalaly caused not by the 

 actual sinking in of that tissue, but only by the hypertrophy of the tissue around it. 



The canker is not only a great disfigurement to the tree, but must seriously interfere 

 with its growth by cutting off a large part of the path along which both water and reserve 

 food must be transported. It is certain, however, that an attacked branch may live and 

 grow for years after the first attack, and perhaps death results only where the branch is 

 completely girdled, and the food and water transportation completely cut off. One 

 branch, with a normal diameter of 13 cm. and a diameter of the swollen part of 20 cm., 

 had only 3.2 cm. of uninjured wood and bark on one side, measured tangentially, yet this 

 branch was alive both above and below the canker that almost girdled it. The capacity 

 of such a branch to transport food and water must be very seriously impaired. 



The only organisni observed that might be the active agent in the production of the 

 canker was a species of Nectria, fruiting bodies of which were scattered over the surface 

 and in the cracks of dead bark around the canker spots. 



On trying to identify the species some difficulty was experienced, as it did not seem to 

 agree exactly with any of the descriptions in Saccardo's Sylloge Fungorum, or Ellis and 

 Everhart's North American Pyrenomycetes. In size of asci and spores it came within 

 the limits of A'^. cinnabarina, but its external appearance was very different from that 

 species. Mr. Preston, an advanced student at the University, has made cultures on arti- 

 ficial media of both N. cinnabarina and the one on the birch, and their cultural character- 

 istics are quite different and constant. So it certainly is not N. cinnabarina. Since this 

 species and also N. ditissima are given credit for producing canker diseases of many trees 

 an attempt was made to identify it with the latter species. Here again the size of the 

 spores and asci agrees rather closely with the descriptions of the various books, except 

 that the spores are wider than the measurements given by Ellis and Everhart. How- 

 ever, comparison wdth the specimens of N. ditissima in North American Fungi, No. 1548, 

 of the latter authors shows plainly that they are not the same. The Nectria upon the 

 birch has larger perithecia, longer asci, thicker spores, and they are of a different shape 

 and more variable in their size, especially the width, than those of N. ditissima examined. 



Superficially the Nectria on the birch resembles N. coccinea (Pers.) Fr., and a close com- 

 parison with the specimens of that species in the University herbarium shows a very close 

 similarity in all points, but they do not exactly agree with the descriptions of N. coccinea 

 in the books. Hence it is deemed advisable to give the description of the Nectria as found 

 on the yellow birch. 



Perithecia single or gregarious, sometimes cespitose, 280-330 mu in diameter, obovoid to 



