184 



that the abnormal growth is produced in response to mechanical 

 exigencies is not unreasonable. Resting as these roots do on a 

 hard, unyielding substratum, the compression strain brought to 

 bear on them when the tree bends in the wind would be much 

 greater than if they rested in soft soil. From a mechanical 

 standpoint the vertical thickening of the wood would strengthen 

 the root against such a strain. Such an explanation is certainl}- 

 in accord with the general idea of the most economical expendi- 

 ture of growth-energy and of material, which, as Haberlandt has 

 pointed out, is as general in the development of trees as in any 

 organisms. 



Barnard College, New York. 



THE BOLETACEAE OF PENNSYLVANIA 



By D. R. Sumstine 



Our state is well represented in the number of species belonging 

 to this family. Nearly two thirds of all the species known in the 

 United States have been reported from Pennsylvania. The fol- 

 lowing is a preliminary list of the genera and species. 



Boletus affitiis Peck § 

 albellus Peck § 

 alboater Schw.f 

 aiiitaccus Morg. § 

 alveolatus B. & C.| 

 Aniericamis Peck * 

 aiiripes Peck § 

 auriporus Peck * 

 badiceps Peck § 

 be till a Schw.f 

 bicolor Peck * 

 bovinus L.f 

 calopus Vx.'\ 

 castaneus l^ull.* 

 clwyse liter 0)1 Fr.* 

 chroinapes Frost | 

 crassipes Peck § 



decorus Frost § 

 diclirous Ellis % 

 edulis Bull.f 

 elegans Schum.§ 

 exiviius Peck \ 

 f elk us Bull.* 

 jlavidus Vw\ 

 fragrans Vitt.§ 

 Frostii Russell * 

 frustulosus Peck § 

 fulvus Peck § 

 glabellus Peck * 

 graei/is Peck' X 

 granulatus L. * 

 griseus I'rost * 

 illudeus Peck § 

 iiupotitus V\\% 



