88G JOURNAL OP FORKSTRV 



confirmation of what Fernald* so earnestly advocates as the result of 

 field investigation — recognition of differences in chemical properties, 

 and of the influence of these differences on vegetation. 



The diagram of soil development, therefore, has a serious limitation. 

 Considering it as representing only soil requirements with regard to 

 physical properties and humus content, the diagram has its value. It 

 shows that beech and sugar maple come at the stage of highest soil 

 development (that is, when considerable humus has accumulated) and 

 have the smallest extent of range. His placing Tsuga canadensis with 

 beech and sugar maple, only slightly below them and with a slightly 

 greater range, may be questioned. In Connecticut and New York 

 hemlock thrives on the rockiest talus slopes — obviously very early stages 

 of soil development — provided there is sufficient moisture from under- 

 ground seepage. He omits Pinus banksiana altogether from the dia- 

 gram and places Thuja occidentalis next to lowest (earlier stage of 

 soil development) with a comparatively small range. Thirteen species 

 are presented. 



The diagram of light intensity also gives thirteen species, though not 

 all the same ones as in the soil diagram. With a few exceptions, the 

 order is about the same as that in the lists of shade tolerance prepared 

 by foresters. The most noticeable exception is the placing of Abies 

 balsamea among the intolerant trees, making it less tolerant of shade 

 (or tolerant of higher light intensity) than Qnercus rubra, Ulmus 

 anicricana, or Betula lutea. Tolerance in Ontario is probably different 

 from tolerance in northern New England and New York, but can it be 

 as different as this? It is also somewhat surprising to see Picea mari- 

 ana classed as less shade tolerant than Ulmus anicricana and Bcfiila 

 lutea. 



The discussions of the individual factors (temperature, water, light, 

 etc.) consist largely of quotations and leave much to be desired. The 

 soil factor is again particularly poor ; he ignores everything but phys- 

 ical properties. 



The humus factor is discussed almost wholly from the point of view 

 of the influence of humus on physical conditions. He seems to ignore 

 the influence upon growth of the nitrogen contained in the humus." 



His explanation of the cause of the northern coniferous region and 



*M. L. Fernald : "Litholo^ical factors limiting the ranges of Pinus banksiana 

 and Thuja occidentalis." Rhodora, Vol. 21, No. 213, pp. 41-67, March, igig. 



° Hesselman : "Studier over de Morrlandska Tallendarnas Foryngringsvillkor : 

 II. Meddlanden Fran Statens Skogsforsoksanstalt," pp. 1121-1286, 1917 (Swedish 

 Exp. Sta.). Review by G. A. Pearson, Jour. For., Vol. 17, No. i, pp. 69-73, iQiQ: 

 also in Jour. For, Vol. 16, No. 8, pp. 937-938. 1918. This paper shows that repro- 

 duction is prevented in certain openings b\' the lack of nitrogen. 



