PERIODICAL LITERATURE 

 BOTANY AND ZOOLOGY 



Perhaps the most extensive investigation on 



Duration this silviculturally in connection with tolerance, 



of aot unimportant subject, has been made by Vinnie 



Evergreen A. Pease, in the State of Washington, near 



Leaves Seattle, a moist (36-inch rainfall), and on San 



Juan Island, a dry station (25-inch rainfall). 



Washington excels in woody evergreens. Of the 52 species in 



western Washington, 16 gymnosperms and 36 angiosperms, the author 



investigated 9 of the former and 22 of the latter, trying to come to 



conclusions, not only as to the actual facts, but as to causes as far as 



possible. 



In the case of species with covered buds, the scars, marking the 

 boundaries of annual growth, were counted to determine the years, 

 in most case on up to 100 specimens of each species ; in case of naked 

 buds, sections through the twigs below the leaves, under hand lens 

 or microscope, served, on up to 50 specimens. On the gymnosperms 

 there were noted the year in which leaf- fall commenced, the year of 

 maximum fall (when twigs were fully half bare), and the extreme 

 duration of the last scattered leaves ; these latter sometimes dead or 

 without color. The data were plotted in curves to secure averages. 

 For determination of causes the series was not complete enough, 

 but a few generalizations the author ventures, which we reprint: 



1. Leaf duration varies widely among the different evergreen 

 species, ranging from Rhamnus purshiana, which in young plants 

 sometimes holds part of the leaves of one season until those of the 

 next season are mature, to Taxus hrevifolia, which has an extreme 

 leaf duration of 23 years. 



2. Leaf duration varies widely in individuals of the same species of 

 different age or growing in different habitats: (0) Saplings have a 

 shorter leaf duration than mature trees in the same habitat. (6) Trees 

 or shrubs growing in the open have a shorter leaf duration than those 

 of similar age in the shade, (c) Trees or shrubs on a windward coast 

 have a shorter leaf duration than those on a leeward coast, {d) Gym- 

 nosperms in a moist climate have a shorter leaf duration than those 

 in a drier climate, {e) A peat bog habitat has an effect similar to 

 a dry climate. 



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