abstracts: botany and forestry 441 



outlined, (1) the blue grama (B.outeloua oligostachya) , the most impor- 

 tant, occupying the higher plains and much of the mountains; (2) the 

 black grama (Bouteloua eriopoda) society, characteristic of the less 

 elevated plains in the southern part of the State; (3) a society intermedi- 

 ate between nos. 1 and 2, best developed in the southeast corner of New 

 Mexico; (4) the salt-grass (Distichlis spicata) society, characteristic of 

 moist alkaline soils; and (5) the Arizona fescue (Festuca arizonica) 

 society, confined to open parks in the higher mountains. The body of 

 the work consists of an annotated list of the Poaceae, Cyperaceae, and 

 Juncaceae of the State, with notes upon their economic importance. 

 Keys are furnished for the identification of the genera and species. 



P. C. S. 



BOTANY. — Three new club-mosses from Panama, William R. Maxon. 



Smithsonian Miscellaneous Collection, 56: no. 29, with 3 plates. 



January 6, 1912. 

 Lycopodium joliaceum, L. stamineum, and L. watsonianum are de- 

 scribed, each being illustrated. All are from the humid forests of the 

 Province of Chiriqui, Republic of Panama. P. C. Standley. 



FORESTRY. — Lightning in relation to forest fires. Fred G. Plummer. 

 Forest Service Bulletin 111. Pp. 41, with plates and diagrams. 

 1912. 



Careful observations on the national forests have shown that lightning 

 ranks second only to sparks from locomotives as a source of conflagra- 

 tion. From early times there has been a belief that certain trees are 

 more likely to be struck than others. Experiments made, both in Europe 

 by Du Moncel and in the United States by the Forest Service, show, 

 however, that no kind of tree is exempt. Laboratory experiments 

 prove that the electric conductivity of wood depends upon its water 

 content. The moisture content of the wood in a tree is subject to great 

 changes. Rain can so wet any tree that it will become, for the time 

 being, an excellent conductor. Thus, tho the moisture content of wood, 

 particularly within the outermost layer of growth in the living tree, 

 favors conduction even the most resinous of trees, with the lowest 

 moisture content, can in a heavy rain become good conductors in a 

 moment's time. 



Trees are the objects most often struck by lightning, because (a) 

 they are numerous; (b) they extend upward and shorten the distance 

 to a cloud, and (c) their spreading branches and roots present an ideal 



