CEPHALOSPORIUM WILT OF ELMS 15 



tested following recovery of the fungus in each instance by infecting additional 

 elms from the cultures obtained. 



In five experiments, young elm trees, four to six feet in height, of each of the 

 following species and varieties were obtained from a nursery and grown in earthen 

 crocks in the greenhouse: Ulmus americana L., U. americana L. (var. ascendens), 



U. campestri.s L., U. glabra L. var. fastigiala Rehd., U. parvifolia Jacq., and 



U. pumila L. 



Experiment 1. 



Procedure: — One tree of each of these species was inoculated, July 15, 1936, 

 in the following manner (Fig. 9): a section of bark on the main trunk was washed 

 with 70 percent alcohol and allowed to dry, then slit vertically with a sterile 

 scalpel for a distance of about three centimeters. The bark was then gently 

 loosened from the wood along each side of the cut and a small piece of bark 

 from a twig medium on which the fungus was growing vigorously was inserted 

 beneath the loosened bark. The wound was bound with sterile wet cotton held 

 in place by a celluloid cylinder. The cotton was kept wet with sterilized water 

 for about two weeks and then allowed to dry out, after which the cylinder and 

 cotton were removed from the trees. Checks were prepared by following the 

 above procedure except that sterile instead of fungus-laden bark was inserted 

 into the wound. 



A duplicate set of trees was inoculated, on the same day, in the manner de- 

 scribed above, but with a slice of agar on which the fungus was growing substituted 

 for the fungus-laden bark. 



Results: — The first trees to show definite wilting were the two American elms, 

 with perhaps a slightly quicker reaction in the tree inoculated from the twig 

 culture than in that inoculated from the agar culture. A month after inoculation 

 the leader of the former had died back for a distance of about 40 centimeters, 

 the other terminal twigs showed some evidence of drying out, and the leaves 

 had fallen from the drying twigs. At the same time the tree inoculated from the 

 agar culture showed similar symptoms except that the leader had died back for 

 only about 30 centimeters. No other trees in the experiment showed any symp- 

 toms at this time. 



The dying back of the two American elms continued throughout the winter 

 and on January 14, 1937, collections were made for cultural and morphological 

 studies. On the first tree the fungus, as evidenced by streaking and growth from 

 tissue plantings, had progressed 13 centimeters upward from the point of inocula- 

 tion and 14 centimeters downward. The following spring new shoots sprouted 

 from the base of the tree, but the trunk had died back to within 20 centimeters 

 of the ground (Fig. 10), approximately 20 centimeters from the point of wounding 

 and inoculation. 5 The second tree was entirely dead at the time of collection, 

 but no streaking was evident and the fungus could not be isolated from the wood, 

 even at the point of inoculation. It was assumed that the death of the tree was 

 due to maladjustment to the unnatural conditions under which it was grown, 

 and this tree was discounted in considering the results of the experiment.^ 



The two trees of U. americana L. (var. ascendens) evidenced some drying 



''In nature, comparable fresh injuries by insects would serve readily as infection courts if the 

 insects themselves were the principal vectors. (Becker 5, 6.) 



"Some of the trees received from the nursery did not grow well in the crocks, but the majority 

 of the trees which were not used in the inoculations showed no ill effects. For this reason, it was 

 considered a fair test to experiment with trees growing in crocks. 



