LSI) JOURNAL OF FORESTRY 



oaks in a key, but without regard to horizon. This arrangement is for 

 convenience of reference rather than the showing of relationships. 

 The text is illustrated with nine plates showing different leaf types. 



The second paper by Dr. Trelease deals entirely with American 

 hybrid oaks. The reviewer is impressed by the large number of re- 

 ported hybrids. In no case, however, has hybridization been definitely 

 established between the black oaks and the white oaks. The author 

 states that in his study of American oaks he has had to account for a 

 considerable number of hybrids, some of which have been described 

 and figured as species in the ordinary sense of the term, while others 

 have been made known by reference to specimens more or less gener- 

 ally disturbed by their collectors. He states that no collective treatment 

 of these forms has been made. They are encountered in herbaria some- 

 times under binomials of their own and sometimes under one or the 

 other of the parental species. 



Two methods of designating hybrids are sanctioned by usage. These 

 methods are illustrated in the naming of the hybrid between Oiioxus 

 alba and Oucrcus priuiis — a common hybrid of eastern United States. 



Quercus alba X prinus.^ 



X Quercus Saulii." 



In the former method the names of the two parent species are made 

 use of ; in the latter the hybrid is designated by an entirely new 

 binomial. 



Each of the indigenous hybrid oaks in the table compiled by the 

 author is designated by a binomial and by the equivalent name derived 

 from the tw'o parent species. More than 125 indigenous hybrid oaks 

 are listed. The paper is accompanied by three plates, showing photo- 

 graphic reproductions of herbarium material. 



J. W. T. 



This paper, by Herbert C. Hanson, gives the 



Leaf Structure results of a year's investigation, beginning the 



as Related to summer of 1915, the purpose of which was to 



Bnvironment determine the exact differences in the structure 



of the leaves in the center of the tree from those 



on the south periphery — that is, shade leaves and sun leaves. The 



work is distinguished from most of the previous investigations by the 



* The ancient oaks of America. Memoirs Brooklyn Botanic Garden, Vol. I, 

 June, 1918, pp. 492-501. 



' Na>ning American hybrid oaks. Proceedings of the American Philosophical 

 Society, Vol. LVI, 1917, pp. 43-52. 



