Origin and Development of the Composite. 213 
fruits were used, anil it was found that between ’66 and 73 the 
relative humidity had no effect on the wind-pressure required. 
Critical Pressure A—*0078 gms. per sq. cm. 1-76 m.p.h. 
Critical Pressure B—'0046 „ „ 1 *35 „ 
It will he noticed that in both cases the figures are higher than 
those for the previous material. The fruits were plumper in the 
variety, but the pappus had about the same development in each. 
The pulvinus in these two cases is the Lactuca type ; the pappus 
hairs are setose-scabrid as in the dandelion, but the pappus is 
sessile, not stipitate as in the latter fruit, and spreads at an angle of 
about 45° with the axis of the fruit, not at right angles to give a flat 
surface as in Taraxacum. 
Tussilago Farfara, L.—This was taken as an example of the 
simple setose pappus with a Tussilago type of spreading (see Chap. 
V, A). As most of the ‘fruits’ are sterile with empty pericarps care 
was taken to choose mature fertile fruits, which were obtained in 
the open. The pappus was too large for the hole in the tube, so 
the fruit was inserted to a distance of 6 cm. before being liberated. 
With the R.H. ’78 or below drying was unnecessary as the pappus 
expanded spontaneously under these conditions. 
Critical Pressure A—-00087 gms. per sq. cm. -59 m.p.h, 
Critical Pressure B—-00081 ,, „ -57 ,, 
It will be noted that the two critical points are very close 
together. The behaviour of the coltsfoot fruit was peculiar. So 
slight is the wind necessary for its dispersal that persons walking 
along the room made sufficient wind to blow the fruit right through 
the tube. Special care was taken, therefore, to carry on the 
experiment on a still day with no one moving in the room at the 
time of the reading, 
It was found that with the fan at the lowest speed, and the 
tube 658-5 cms. away, the fruit was blown right through the tube 
sometimes with, sometimes without, pauses. At a distance of 703*5 
cms. the fruit remained motionless for about five minutes and then 
moved a distance of 5-40 cms. The critical pressure B is therefore 
too high, but it was not possible at the time to carry the experiment 
further, as a complete absence of external currents of air is neces¬ 
sary for the accurate determination of the constant in this case. 
Centaurea imperialism Hausskn.—This was taken as an example 
of a heavy fruit with a pappus of numerous paleaceous setae. The 
spreading of the pappus is accomplished by means of a pulvinus to 
each seta, the Cirsium type of Taliew (see Chap. V, A). As 
