324 Kansas Academy of Science. 



a tunnel at its upper end. The pressure of the mercury compresses 

 the air in the short arm, forcing it through the twig and causing it 

 to appear as bubbles wherever there are openings in the twig. The 

 more minute the openings the greater the pressure required to pro- 

 duce bubbles at a visible rate. It is indeed true that when bubbles 

 are obtained at a greater pressure they can also be obtained, more 

 slowly, however, at lesser ones. So it is an exceedingly diflBcult 

 matter to obtain an accurate comparison between different subjects, 

 but my data enabled me to group them roughly into four classes. 

 Class A consists of those in which the passage of air is least ob- 

 structed, so that bubbles were readily obtained with a pressure of 

 10 cm. or less of mercury. Class B comprises those in which 10 

 t6 50 cm. was used to form the bubbles; class C those in which 

 they were noticed at higher pressures (50 to 140 cm.), and class D 

 those in which none were obtained by the highest pressures applied, 

 which varied in difPerent cases from 90 to 140 cm. and was generally 

 maintained for a considerable length of time. 



One hundred twigs belonging to thirty-five different species were 

 tested between October and January, after the season's growth had 

 ended and mostly after the leaves had fallen. The results were as 

 follows, a number in parentheses following each species in which 

 the same result was obtained from more than one twig. 



Class A. — Salix alba, Hicoria ovata, Gymnocladus canadensis, 

 Rhus copallina (2), Jilsculus arguta, Acer saccharinum, Acer sac- 

 charum (2), Asimina triloba (2). Eleven twigs of eight species. 



Class B. — Salix alba, Populus deltoides, Quercus acuminata, 

 Corylus americana, Tuglans nigra, Hicoria ovata, Ulmus fulva (2), 

 Ulmus americana, Celtis occidentals (3), Plantanus occidentalis, 

 Fraxinus lanceolata, Sambucus canadensis (2), Prunus americana 

 (3), Grleditsia triacanthos, Gymnocladus canadensis, Amorpha fruti- 

 -cosa, Rhus aromatica, Ailanthus glandulosus, Acer negundo. 

 Twenty-six twigs of nineteen species. 



Class C. — Juniperus virginiana, Populus deltoides, Juglans 

 nigra, Ulmus americana, Celtis occidentalis (2), Toxylon pomiferum 

 (2), Plantanus occidentalis, Catalpa speciosa, sanbucus canadensis, 

 Prunus cerevisiese, Gleditsia triacanthos, Gymnocladus canadensis 

 (3), Cercis canadensis, Rhus glabra (3), Xanthoxylum americanum 

 (3) , Acer saccharinum (2) , Acer negundo (3) . Twenty-eight twigs 

 and seventeen species. 



Glass D. — Juglans nigra, Ulmus americana, Catalpa speciosa, 

 Cornus asperifolia, Prunus americana, Prunus persica, Pyrus coro- 

 naria, Gleditsia triacanthos (3), Cercis canadensis (2), Rhus copal- 



