44 
THE PLANT WORLD. 
room. Bryophyllum crenatum has the advantage that the entire 
upper end of the hitherto strongly orthotropous leafy shoots be¬ 
come reversed in position as soon as the formation of the inflores¬ 
cence begins, until finally the tip of 
the axis becomes directed downwards. 
By reversing the- plant, it is easily 
shown that here is an example of posi¬ 
tive geotropism. When the flowers 
are further developed, changes take 
place which result in the resumption 
of the upright position, that is, the 
negatively geotropic one. 
The plant in question (which may 
be obtained from dealers) is easily 
cultivated, more so indeed than Bryo¬ 
phyllum calycinum, and is of further 
interest on account of the fact that 
it too produces buds on the leaves. 
It therefore well deserves a place 
among the useful materials of the botanical laboratory. (K. 
Goebel. Flora, 94: 205. 1905. Translated by F. E. L.) 
The Relation of Salts to Natural Vegetation.— Dr. Bur¬ 
ton E. Livingston (Bot. Gaz. 39: 22. 1905) has continued his 
former studies of this subject in Roscommon and Crawford 
counties, Michigan. Two general types of vegetation are dis¬ 
tinguished : 
(1) The Upland Type, consisting of (a) hardwood type; (b) 
white pine type; (c) Norway pine type; (d) jack pine type. 
(2) Lowland types, comprising (a) open meadow type; ( b ) 
tamarack-arborvitae type ; (c*) mixed swamp. 
His researches lead the author to the conclusion that forest 
distribution in the region studied is a function mainly of the size 
of soil particles. “ The size of particles determines the amount 
of air and moisture in the soil, and these in turn determine the 
amount of humus formation and the growth of nitrifying organ¬ 
isms, and perhaps also to a certain extent the amount of soluble 
salts in the surface layers.” 
Fig. 15. —Positively geo- 
tropic shoot of Bryophyl¬ 
lum crenatum as flowering 
begins. 
