84 BOTANICAL GAZETTE [JANUARY 
use of water movement. Whenever transpiration is occuring, a “saturation 
deficit” i is produced in ba cells of the region transpiring. This is the source 
of the “sucking power.” When the loss of water is So great that the protoplast 
to be the case. The method for getting the exact estimation of the greatest 
suction existing was ingenious. A twig that offered at one region great resist- 
e to the movement of water (the resistance secured by tight clamping, 
aehe eesting, or blocking of tracheae) was placed in a potometer. At a 
time when no “saturation deficit” existed, a determination was made of the 
rate of flow produced in the potometer by about 60 cm. of Hg. artificial suction. 
Through rapid transpiration the greatest “saturation deficit” was allowed to 
develop and the rate of flow it produced observed. The amount of suction 
involved in the second case could be figured from the known suction of the 
first, for it was found that the rate of flow was proportional to the suction. The 
maximum suction produced in forms like nga and Helleborus ranged 
from 10 to 20 atmospheres.—WILLIAM CROCKER 
Sand dunes of Illinois.—Gtrason’ss study of the vegetation of the sand 
deposits of Illinois is one of the most careful ecological surveys yet made of 
any region upon the continent. These deposits represent the most extensive 
areas with natural vegetation in the state, and cover over 8000 s 
two most important types of vegetation are the grass lands, of which the bunch 
grass association, formerly covering nine-tenths of the entire sand area, is 
still conspicuous, and the forest, in which the black oak forms the typical 
association. This forest association, together with those composed of other 
species of oak which succeed it, are discussed elsewhere in some detail by Hatt 
and INGALL”, who give more emphasis to the economic than to the ecological 
aspect. It seems evident that the forest is slowly encroaching upon the prairie, 
although the advance of the oaks presents several unsolved problems. This 
tension line between forest and prairie is but one expression of the diverse 
elements of vegetation here in close contact, showing the unique position 
occupied by Illinois as a meeting ground for the great vegetational provinces 
of the north, south, east, and west. 
Not only have the larger relationships existing between formations and 
associations received attention, but a careful analysis of the composition of 
each association is made, and the i importance of the various constituent species 
estimated by the detailed study of many a An extensive list of these 
species is well annotated—Gro. D. FULLER. 
*s GLEASON, H. A., The vegetationof the inland ye — of Illinois. Bull. 
Tl. ae Lab. Nat. Hist. 9: 23-174. pls. I-20. figs. 6. 
L, R. Cuirrorp, and Incatt, O. D. Peed EET in Illinois. Bull. 
Til. a Takk Nat. Hist. 9:175-253. ror1. 
