488 General Notes. [ August, 
TABLE VIL 
From 0 to 5° East, 18 leaves. From 0 to 5° West, 9 leaves. 
s 50 to 10° e 8 “ “ac 50 to 10° e 5 “ 
“ 10° to 15° “se ey “ “ 10° to 15° é 3 “ 
m doS de DPS Hib. R A ROS cca cn ee 
a ee eee mE ROT Oe ee 
FS DONES OT gto LEONG HOP NOTE A 
e 300 to 350 e 1 “ e 30° to 35° “ 5 “ 
“ 35° to “ 3 “ é 35° to 40° “ 2 “ 
a eae EO a Pte rT 
Sale to WM he BOE GON Soa 
. 28, Bee © goaid soe) e 
“ 55° to 60° s 0 “ a4 55° to 60° “cc 1 “ 
“ec 60° to 65° “6 0 “ “ 60° to 65° “ 1 “ 
Oe Too 0 "i meaig iiit. E A ce at 0 5 
“ec 70° to 75° “ 0 “ (23 70° to 75° “ ] “e 
ae tO O re 0 ss TOn Ben 0 Ke 
BOC Wh eer. S 1 bd en B09 to BHO Ae 0 n 
C oe o = B95 to D00. o ei: 
Total leaves East, 54. Total leaves West, 39. 
In one case (Table VI. in part) of twenty-eight leaves examined, all 
but three had rotated upon their petioles in assuming their positions, 
that is, they twisted their petioles; of these twenty rotated with the sun, 
and five against it. Of the three remaining leaves, two rotated their two 
half blades upon their midribs, so that both edges tended to point towards 
the north ; the remaining leaf did not show any evidence of rotation in 
either direction, and its bearing was seven degrees east of north. 
In another case (the second leaf in Table I.) a leaf was found to have 
rotated through at least 270° of arc to reach its final position. Origi- 
nally it stood with one edge nearly due east, and the other west; the 
western edge then rotated northward, passed the zero point and swung 
away round to the south, passing 1°45! beyond that point. This rotation 
was all confined to the petiole. 
How to account for this evident turning has been, and still is a puz- 
zling thing. In order to see whether there was any diurnal rotation, oF 
turning, such as is observed in the sunflower, I carefully set stakes 1n 
line with several leaves having quite different bearings, and wate 
them closely for about a week, but failed to discover the least tendency 
to any such motion. 
Dr. Gray, I believe, first made the suggestion that the structure of 
the leaf must have something to do with their so-called “ polarity,’ and 
made some examinations as to the number of stomata upon the two sur- 
faces. I have made many examinations by the aid of the microscope, 4? 
have determined that in the central part of a full grown leaf the stomata 
are at the rate of 52,700 to each square inch of upper surface, and 56,- 
300 to each square inch of lower surface. In this calculation I made no 
account of the veins, which apparently occupy an equal area on both sur- 
faces, They probably take up fully one half the surface, and they are 
destitute of stomata. i 
Five years ago I examined the two surfaces of quite young leaves» — 
