1912] CURRENT LITERATURE 261 
can endure drying for about a half year at least. The algae endure large 
amounts of moisture, perhaps better than the lichen hyphae, but the hyphae 
endure dryness better than the algae. It would add greatly to the value of 
the research if the cultures could be kept long enough to ascertain the time 
and conditions necessary for the development of podetia and apothecia.— 
Bruce FINK. 
Light in relation to tree growth.—A recent bulletin from the Forestry 
Service, by Zon and GRAVES," will be welcomed by botanists and foresters as 
a valuable addition to their literature. The authors first show the influence 
eafing. An 
interesting table is ae showing the decrease of both direct and diffuse light 
whereas diffused light is 20. At the equator direct fight i is 489 as against 227 
for diffused light. The réle of direct and diffused light in treés and forest 
attention, considerable data on this topic being cited from WIESNER’s well- 
known researches. 
e greater part of the Bulletin is devoted to tolerance, the ability of 
plants to endure shade. The factors affecting tolerance and the methods of 
determining it are fully discussed. The results of LuBrmENKO and of GRAFE, 
dealing with the effect of sensitiveness of the chloroplast and of anatomical 
structure upon tolerance, are briefly stated. There is also a statement of the 
influence of climate, altitude, soil moisture, soil fertility, and age, vigor, and 
origin of the trees upon tolerance. Lists of trees are given showing the order 
of tolerance as determined by various European and American workers 
Finally, the methods of determining tolerance are considered under thee 
heads: (1) empirical methods; density of crown, self-pruning, num f 
branch orders, natural thinning of stand, conditions of reproduction, SSisive 
height, and artificial shading; (2) anatomical and physiological methods; 
structure of leaves and assimilation capacity of leaves; and (3) p hysical 
me i f 
chemical light intensity. The authors emphasize the general agreement in 
order of tolerance of various species as determined by the empirical and by 
other methods. They also point out the weak points in the various methods, 
One feels that ZEDERBAUER’S luminous light method is underrated; while 
WIESNER’s photochemical method, with its evident shortcomings, is over- 
N, RAPHAEL, and Graves, Henry S. ler in relation to tree growth. U.S. 
Dept. pends Forest Service, Bull. 92. pp. 50. 
