Pflanzenkrankheiten. 281 



Stakman, E. C. and M. N. Levine. Effect of certain ecolo- 

 gical factors on the morphology of the urediniospores 

 of Puccinia graminis. (Journ. agr. Research. XVI. p. 43— 77. Jan. 

 13, 1919.) 

 Extensive experiments were carried on for about fwo years for 

 the purpose of determining the effect of hosts and of physical fac- 

 tors upon the morphology of urediniospores. It was found that 

 congenial hosts of any biologic form have no perceptable influence 

 on the morphology of the spores, negative results being obtained 

 both when the same biologic form was grown on several different 

 hosts and when several different biologic forms were grown on the 

 same host. Unfavorable physical factors or an uncongenial host 

 have a tendency to decrease the size of the urediniospores but as 

 soon as the unfavorable factors are removed the spores regain 

 their normal size and structure. W. M. McDougall. 



Stevens, F. L. and J. True. Black spot of onions sets. 

 (Bull. N° 220, Illinois Agr. Exper. Sta. p. 507—532. f. 1—19. May, 

 1919.) 



Contains as new: Cleistothecopsis n. gen. (Perisporiaceae) , with 

 C. circinans; and, for the conidial form of this, Volutella circinans 

 ( Vermicularia circinans Beck.). Trelease. 



Stewart, A., A consideration of certain pathologic con- 

 ditions in Ambrosia trifida. (Amer. Journ. Bot. VI. p. 34 — 46. PI. 

 1. Textf. 1. Jan. 1919.) 



The structural changes brought about in the stem by two gall 

 producing organisms, one a fungus and the other an insect, are 

 compared with the structural characteristics of traumatic tissue. 

 "The most marked similarities between the structure of the fungus 

 gall and that of traumatic wood are in the presence of bündle 

 ellipses and in the reduction in number and size of the vessels. 

 Similarities between the insect gall and traumatic wood consist in a 

 greater radial growth of xylem, resulting in a more distinctly 

 woody growth than takes place normally.' 1 The violent misplace- 

 ment of cells so common in traumatic wood is but little evident in 

 the fungus gall and not at all in the insect gall. 



The Stimulus from the fungus is much stronger than that of 

 the insect and is able to overcome and neutralize the latter when 

 the two organisms are present in the same tissue. On the other 

 hand the fungus is able to influence growth only where the fungus 

 is actually present in the tissue while the insect exerts an influence 

 on growth in all parts of the stem which are in close proximity to it. 



W. B. McDougall. 



Stewart, V. B., A twig and \e af disease of Kerria japonica. 

 (Phytopathology. VII. p. 399-407. f. 1-7. Dec. 1917.) 



Contains description of the new species Coccomyces Kerriae, as 

 causative. Trelease. 



