1897 } CURRENT LITERATURE 293 
Three classes of pathogenic material were used in these investigations : 
(1) frosted conifers; (2) witch brooms on different species of Abies produced 
by the growth of £cidium elatinum ; and (3) tissues of conifers that had been 
infected with Agaricus melleus, Pune abietina, or Pestalozzia Hartigii. 
In the first case tissues from Pinus sylvestris, Picea excelsa, and Chamecy- 
paris Lawsoniana were used. When twigs of P. sy/vestris are frosted but 
not killed their tissues sometimes lose their power of becoming turgid and 
the shoots therefore tend to remain in a drooping position. By renewed 
growth near the tip of the branch the apex again assumes to a greater or less 
degree an upright position. Where this renewed growth takes place, on the 
under side of the branch a large amount of the tissue formed is similar to the 
“red wood” formed on the under side of normal hyponastic branches of 
Pinus Strobus and Picea excelsa. In both cases there are fewer resin ducts on 
the side of the twigs having ‘‘red wood” thanon the other. “Double rings,” or 
‘frost rings,” are sometimes formed in the two, three, or four-year-old 
parts of frosted pine shoots. In such cases there are generally no vertical 
resin ducts in the inner half of the annual ring. This is true also of Picea 
excelsa. The annual ring, with frost ring, in this species is essentially 
like that of Pinus sylvestris so far as structure, number, and distribution of 
ducts is concerned. In some instances, where,the frost ring is formed late or 
where two are formed in one season, there may be developed a complete 
circle of resin ducts in the frost ring itself. Resin ducts are abnormally 
formed in the bast in twigs of Chamecyparis Lawsoniana as a result of frost- 
ing in late spring. The ducts are formed where the cells have been forced 
apart by the formation of ice masses between them and they have failed to 
return to their mecine position after the melting of the ice. 
tively shorter. The diseased twigsdevelop very early as do the needles upon 
them, while the normal ones are much later. The latter are much thicker 
and about one-half the length of the normal leaves. In 4. firma the dis- 
eased needles do not fall in the autumn, while in 4. fectinata they do. In 
both the needles show no transverse heliotropism. The buds are relatively 
larger than those of normal branches; they have a greater number of scales 
but these are smaller than in the healthy bud. The resin ducts in the 
diseased bud scales have the regular form, but they are either abnormally 
large or abnormally small and have fewer and more irregular epithelial see 
than have the normal scales, The mycelium of the fungus | 
: parts of the tissue. except the cavity of the ducts and the epithelial eels. 
Generally there are fewer stomata and trichomes and — —* 
