1900] GEOTROPISM OF STEMS 195 
Ceteris paribus, however, the more rapid growth of the lower 
half would depress its turgor,‘ so that the equality observed indi- 
cates that with equal growth the lower half would have its turgor 
raised. It was noticeable that in general the relation of turgor in 
pith and cortex was the same in both halves (as in the growing part, 
in the figures just given); although to bring a pressure to bear 
against the tube which kept them straight, one half should mani- 
fest an excess of turgor in the cortex, the other rather in the 
pith. I do not know whether or not the entire stems would 
show any difference in the turgor of the halves, such as Pfeffer 5 
observed in some grass nodes; but they do exert an upward 
pressure by the elimination by growth of the tension between 
the walls and cell-sap of the under side, so that the osmotic 
pressure is available for outside work. If a hypocotyl of Lupinus 
be removed from a horizontal glass tube and immediately split, 
the lower half stretches out, often at least 2™™ longer than the 
upper, and this difference is maintained after entire plasmolysis. 
To determine the effect of the position of the horizontal 
half-stems on the rate of growth, as compared with the normal 
upright position, I paired a number of plants, split them, matched 
the halves of each plant with those of the other plant of the 
Same pair, put them into glass tubes, and placed one tube erect, 
the other horizontal. Then one half of A and one half of B were 
erect; the other half of A was horizontal with the split surface 
up, and the other half of B was horizontal with the split surface 
down. They were wrapped in moist filter paper, and except for 
their position with regard to gravity were under as like condi- 
tions as could be desired. Of a series of six plants treated in 
this way, the growth of the erect halves in two days averaged 
7™. The growth of the horizontal halves, whose cut surface 
was downward averaged 6.8™™. At the same time the comple- 
mentary six plants averaged: the erect halves, 8.1™", and the 
horizontal halves, with split surface up, 17.1™. Dec. 8, ten 
*CopELAND: Ueber den Einfluss yon Licht und Temperatur auf den Turgor. 
Inaug.-Diss. Halle a. S. 1896. 
5 PFEFFER: Druck und Arbeitsleistung durch wachsende Pflanzen. 
