Although broken bmnches and bqsanch stubs are t h e m o s t frequently encoz~ntered external signs of defects in the t?.unlc of yellozu birch, t h e y zue?.e found t o be

Analysis of relevant data for the last 11 years improved the precision of zoning for white pine vulnerability to blister rust in Quebec. The validity of the existing approach for the area under study was confirmed. White pine located in zones 1 and 2 usually indicated less than 15% stem infections by the blister rust. Distribution of the white pine weevil damage in the zones is presented. Key words: Pinus strobus L., Cronartium ribicola J.C. Fisher, Pissodes strobi Peck, blister rust vulnerability.

Four host-susceptibility zones based on elevation and climate were delineated. In zone 1, less than 5% of white pine stems were affected even without Ribes eradication. The level of infection remained lower than 15% in most plantations in zone 2. Recommendations based on recent studies are made concerning site selection and protective measures. Studies of meteorological data and of recent and earlier disease surveys confirm the validity of this approach to the white pine blister-rust problem.

Xylem of sugar maple and yellow birch trees were exposed to natural infection by making axe blazes to simulate mechanical injuries. After 8, 21, and 34 months, dissection and isolations made from the discolored wood permitted the localization of certain microorganisms in three arbitrarily determined zones. Longitudinal and radial development of discoloration associated with wounds was more rapid in yellow birch than in sugar maple. There was evidence of a succession of organisms in the colonization of the wounds which was subsequent to the first discoloration process and involved different organisms in the two hosts. In general, decay fungi did not appear until after 21 months. Cytosporadecipiens occurred exclusively in discolored wood of sugar maple while Phialophora spp. and Cephalosporium sp. dominated the discolored wood of yellow birch. Bacteria were more frequent in yellow birch than in sugar maple. Relationships between size of injuries, linear extent of the discoloration produced, and identity of the various organisms involved are also presented.

Resume D a n s les d e u x localite's oil l'dtz~de fut e f f e ctue'e, les blessures me'caniqz~es, les ge'livures e t les grosses b r a n c l~e s casse'es e'taient les points d'entre'e souvent responsables d e s car i e s les plus v o l z~m i n e u s e s t r o u v k e s d u n s le t r o n c cle l'e'?.able a sucye. D a n s zLne ?ne"nze cate'gorie cle blessures, le v o l u m e nzoyen de l a carie a z~g m e n t a i t lorsque les climensions d e s blessures e'taient plus grandes. C e s clonne'es o n t s e r v i ci l'e'laboration d'un systhme de classification d e la qz~alite' d e s a?.bres e t ce systhm e semble app?.oprie' pour kvaluer les pertes a v a n t la coupe. Abstract I n b o t h localities zuhere t h e dissections w e r e p e r f o r m e d , mechanical i n j u r i e s , f r o s t cracks a n d large b r o k e n branches w e r e f o u n d ~e s p o n s i b l e for t h e e n t r y of m o s t of t h e extensive d e f e c t s in t h e t r u n k of living s u g a r maple. Within an i n j u r y class, t h e average v o l u m e of cull following large i n j u r i e s w a s greater t h a n t h a t follozuing small injuries. A quality classification s y s t e m i s presented a n d s e e m s appropy-iate for a cull e s t i m a t i o n bef o r e cutting.