PAMPTNG-OFF IN FOEFST NURSERIES. 37 



parasitic on pines in preliminary inoculation experiments (62). In 

 1910 Spaulding (137) found it on spruce in New York, and Hof- 

 mann (76) later made successful inoculations on both pine and spruce 

 seedlings, using P. debaryanum cultures both from aerial trap plates 

 and from recently damped-off seedlings of cabbage, radish, and 

 Russian thistle {Salsola tragus). Hofmann's work, detailed notes of 

 which the writer has been permitted to examine, was done with cul- 

 tures which were contaminated by molds, but was checked up by 

 microscopic examination of the lesions resulting, which showed the 

 affected tissues filled with nonseptate hyphae. His results are taken as 

 a rather strong indication that P. debaryanum attacks spruce as well 

 as pine and that the fungus attacking conifers is physiologically as 

 well as morphologically identical with that causing the damping-off 

 of angiosperms. 



There thus appears from the literature to be reason to believe that 

 Pythium debaryanum, is parasitic on representatives of two groups 

 of the Pteridophyta and on gymnosperms, as well as on various 

 monocotyledons and dicotyledons, a range of hosts not only remark- 

 able but perhaps unequaled in our present knowledge of plant 

 parasites. Final published proof of parasitism seems to be available 

 for three or four species of dicotyledons only. Additional inocula- 

 tions on conifers with strains isolated from various other hosts are 

 reported in the present bulletin. Some of the detailed evidence neces- 

 sary for complete proof of the parasitism of the Pythium on conifers, 

 lacking in experiments previously reported because of the doubtful 

 purity of the cultures used and failure to reisolate and reinoculate 

 with the organism, is also given here, together with evidence of the 

 ability of the parasite to cause root sickness of pines too old to suffer 

 from damping-off. 



Descriptive data of interest on Pythium debaryanum have been 

 supplied by Hesse (74), De Bary (5), Ward (144), Miyake (89), 

 Butler (23), and Butler and Kulkarni (24). An important contri- 

 bution to the physiology of the fungus and the factors controlling its 

 passage through the tissues of one of its hosts has recently been made 

 in the previously mentioned paper of Hawkins and Harvey (71). 



IDENTITY AND ISOLATION. 



The fungus in the writer's cultures referred to Pythium debary- 

 anum Hesse has been so called for the following reasons : 



(1) The morphological characters agree with those described and figured for 

 Pythium debaryanum by other workers and with those of strains obtained from 

 Dr. H. A. Edson under this name. 



(2) The absence of zoospores in the writer's cultures agrees with the experi- 

 ence of others with Pythium debaryanum (2, 5, 23, 24, 38, 100), all workers 

 with pure cultures having obtained zoospores infrequently, if at all. The 

 earliest work by Hesse (74) in which zoospores were apparently produced 



