Origin and Development of the Composite. 217 
VVt. of 100 fruits=0756 j»ms, 
average weight of one fruit=’000756 gms. 
This is of the same magnitude as Bessey’s figure and the 
difference is possibly due to the fact that the fruits used were very 
well developed. 
Area of Pappus Surface. The constant referred to by this 
name is not the sum of the areas of the exposed surfaces of the 
hairs as calculated by Dandeno (9) but the area covered by a circle 
with a diameter equal to twice the length of a pappus hair. The 
pappus from eight fruits was stuck to paper and measured under a 
dissecting microscope. The longest hairs and the mass of hairs 
were both measured. 
Diameter in mm. as measured by the longest pappus hairs= 
12-5, 12 0, 12-0, 12-0, 12 0, 12-5, 12-0, 12-0. Average=12-12 mm. 
Diameter in mm. as measured by most pappus hairs=12'0, 
1T5, 11*5, 1T5, 1T5, 12-0, 11*5, 1T5. Average=lT62 mm. 
As the efficiency of the pappus would seem to depend on the 
surface formed by the mass of pappus hairs rather than upon the 
few longer hairs, lT62mm. was taken as the average diameter of 
the pappus surface. The average area of the pappus surface, 
therefore, is 1-06 sq. cm. 
Angle of the Axis. As the fruit was in movement during 
dispersal observations were not accurate. The angle of the axis 
with the horizontal appeared to vary between 45° and 60°. 
Photographic measurement should be possible and will be used in 
subsequent experiments. 
Rate of Fall in Quiet Air. The determination of this constant 
by Praeger (30) is taken as sufficiently accurate and is converted 
into m.p.h.; 12 feet in 8 5 seconds—*98 m.p.h. 1 
The Vertical Component. In the experiments described in 
Section B the wind was always lateral, so that a wind with the 
minimum or critical vertical component also had a horizontal 
component. Any wind-pressure which lifted the fruit when it had 
once fallen was, therefore, due to a wind, the total force of which 
exceeded the critical vertical component. This component is taken 
to be the pressure of the maximum wind which does not blow the 
fruit more than 4 cm. (see below under Winds between “ W ’' and 
“ V ”). The chief source of error in the experiment is the friction 
1 This is calculated from the rate of fall (12 feet in 8 - 5 seconds) re¬ 
corded by Praeger. He gives inversion of the time and multiplication by 8 
as a method for approximating in m.p.h. the observed rates of fall in secs, 
per 12 feet. A closer approximation is obtained by using 8 - 4 instead of 8 
and this has been used in the present calculations. 
