Origin and Development of the Composite. 219 
the method of Dingier and Praeger than by the rather tedious 
method adopted in the present investigation. 
The Critical Vertical Component. Although the pressure and 
the velocity equivalent to the pressure of the critical vertical 
component can he calculntd as shown in Section B from the known 
pressure of the maximum wind which does not move the fruit, the 
actual value of the pressure on the pappus can he determined only 
when the area of the pappus is known. This constant as shown 
above is F06 sq. cms., therefore the pressure of the critical vertical 
component on the area of the pappus is -0026 x 1 , 06= , 002756 gms. 
The Efficiency of the Pappus. If the pappus acted as a con¬ 
tinuous membrane the total pressure of the critical vertical 
component would he equal to the weight of the fruit, hut the 
hairs of the pappus do not form a continuous membrane. Some 
of the wind passes between the hairs and exerts no effective 
pressure. The pressure actually exerted on the pappus by the 
critical vertical component, is, of course, equal to the weight of the 
. .. ,, . c .. pressure actually exerted on the pappus 
fruit, so that the fraction -i-———-——*-——— 
pressure of V on the area of the pappus 
gives the efficiency of the pappus as a sail or wind-holding 
mechanism. 
This efficiency is, therefore, 
•000756 
•002756 
The Minimum Wind for Dispersal. In discussing the resolu¬ 
tion of the pressure in Fig. 27 the fruit was regarded as stationary, 
but it is in motion during dispersal. The point of view upheld by 
previous investigators is that the fruit rapidly attains the velocity 
of the wind which is dispersing it. A little, consideration of the 
diagrams in Fig. 27 will make it quite clear that H, the horizontal 
component, is considerably less than M, the total pressure, when 
the fruit is at an angle of 45°. If the fruit were vertical, H would 
be eliminated and the mechanism would act only as a balloon. On 
the other hand if the fruit were almost horizontal ( i.e. the pappus 
almost vertical) V would be small compared with H. Even in the 
latter extreme case, however, although H would be almost equal to 
M, the efficiency of the pappus being only *27, the horizontal com¬ 
ponent H would have only the effect of M X '27. It is clear then 
that, even when H attains its maximum value, the velocity at 
which the fruit would be blown would be less than the velocity of 
M and therefore the fruit would never attain the velocity of the 
wind. 
From the preceding data it is possible to calculate the 
minimum wind required for dispersal of the fruit to a distance which 
