r.'::«>| DISEASES OF PLANTS. 249 



fnuiiil <iii Kihcs ill scvcM'iil States has hctni uU'iititifil as CioiKirliitni ixiiih iilalc, 

 llic altiM-iiati' stajii' of a IVridonniuiii ncfiirring on the piuoii piiu', Iml hannU'ss 

 to wliitt' piiu'. Kihfs pii'seiits Go specit's indigenous t«» western Nortii America, 

 sliowini; a ranj,'e of athiptatioii to nearly every site condition occurriiiK in these 

 rejiions. and fiirnisliiiij; unlirokcii cliains for the dissemination of white pine 

 hiister rust. A sununary is ^'iven of the Kihes eradication data in tlie Norlli- 

 eastern States during r.»lt>. 



Scientific r«>searcl« in I !) 1 1> [on white pine blister rust), I'. Si'Aii.niNO 

 (1 ;//<•/•. I'liuit I'csl Cum. Bui. J, ilDlO\, pp. 10, //).— Investij,'ations durinj,' lltl'J 

 were carried out in a manner siniiUir to those of the previous year (E. S. 11., 41, 

 ]i. .'Jni), being conducted principally by H. H. York at North Conway, N. H., 

 and K. II. I*enninj,'ton at Lewis, N. Y. 



York found that aeciospores may be blowni apparently for a distance of ITi or 

 I'll nnles, and may be carried up 5,()dO ft. still reniaiidng viable, other data re- 

 pirdin},' the viability of spores are given from which it was concluded that the 

 character of the vegetation intervening between the Kibes and pines and the 

 climatic conditions are vital factors in the distance across which sporidia may 

 couununicate the disea.se. 



I'eiuiington found the general conditions in the Adirondack section not quite 

 .so favorable for the distribution of spores as they were in the White Mountain 

 section. The amount of infection of pines depends upon weather conditions, be- 

 ing favored by cool, moist situations i)rotected from winds. In general, the num- 

 ber of infections in pine varies directly with the amount of Ribes h'af surface 

 and inver.sely as the square of the distance from Ribes. Investigations on the 

 cutting out of infections in pines was started in 1917 by I'osey and Gravatt, 9<> 

 infections being thus treated. It is said that where the cut was made at 1^ 

 in. distant from the affected part, the disease has not again reappeare<l. 



Unless the conditions are exceptionally favorable for transfer of spore.s, 200 

 or oOU yds. is a sufficient distance to prevent infection of the pines by spores from 

 Ribes. The cultivated black currant (Kihes nigrum) seems to be the most dan- 

 gerous species in this connection. 



Overwintering by means of aeciositores in cankers on pines and also l)y ure<li- 

 iiiospores r)n infected Ribes leaves has been prove<l. Quantity of infection of 

 jiines depends to a great extent upon the volume of spores produced by the in- 

 fecting currants. The etliciency of eradication of Ribes depends u|)on the rela- 

 tiv«' icduction of Ribes leafage, upon which directly dei)ends the quantity of 

 spores given off to infect piuQs. 



Ai-tificial infection of pines with Cronartiuni ribicola, G. P. Clinton and 

 F. A. McCoKMicK (Amer. Plant I'tnt Com. Bui. ^ [1019], p. 12). — This is a re- 

 I'ort of results of artificial infection of pines along the .same lines as reported 

 previously by Clinton (E. S. R., 41, p. S't'Z). 



Successful inoculations have been made on more than 150 young junes, 

 >iiiiiething like 1(),(>(M) distinct infections having been secured, showing conclu- 

 sively that infection takes place through stomata of the leaves. The first 

 visible sign of infection is a ndnute yellow spot centering over the lines of tlie 

 stomata on the under side of the leaf. Under greenhouse conditions the.se 

 become evident within tliree months after inoculation, infection occurring within 

 124 hours. Leaves less than two years old have been abundantly infected. 

 Within the stomatal cavity of infected leaves the ft)rination of a peculiar 

 swollen body occurs, from which a single hypha runs downward and soon 

 gives rise to relatively large sclerotial bodies. The mycelium then extends 

 into tlie vascular bundle of the leaf, which it follows downward until it 

 readies the twig, progress being quite rapid under conditions fav«uable to 

 plant growth. 



