76 TRANSACTIONS, NATUEAL HISTORY SOCIETY OF GLASGOW. 



advantage that this only occurs on days when the 

 wind is sufficiently strong to bear them some distance 

 away. To promote in this way the waving to and fro 

 of the dehiscent fruit, with the object of scattering 

 the seeds, is doubtless also the use of the inflated 

 persistent calyx of Rhinanthus and Silene infiata. 

 The large capsules of Papaver, Iris, Tulipa, Scilla, 

 and several Carnpanulce are admirably adapted to 

 have their seeds shaken out by the wind in this 

 fashion. Another point of interest is well illustrated 

 in the genus Campanula. Some species have upright 

 capsules ; these dehisce at the top. Others with an 

 inverted capsule discharge their seeds through 

 openings at the base of the capsule near the flower- 

 stalk. The arrangement in both cases prevents the 

 seeds being emptied out together ; otherwise they 

 might fall straight to the earth and form a heap at 

 the base of the plant. 



The blade of the wing, in most cases, is either 

 slightly twisted or set at such an angle that the 

 fruit or seed in descending does not fall perpen- 

 dicularly, but either flutters slowly down, shoots 

 aside, rotates, or eddies round in circles. By this 

 simple arrangement the velocity of its descent is 

 diminished ; the seed will be longer exposed to the 

 wind's action, and carried in consequence to a 

 greater distance. A seed or fruit with vertical 

 evenly-set wings, if it should happen to fall with 

 these appendages presenting their edges to the 

 direction of the wind, would reap no advantage 

 from their presence. But if the wings be set 

 obliquely this cannot happen, for even in still air 

 the seed in descending begins to rotate on its axis, 

 and thereby brings its wings broadside on to the 

 wind. If the seed revolves round its horizontal axis, 

 it will appear to flutter, and will have the full 

 benefit of any ascending current. This explains why 

 these whirling and gyrating seeds are so easily 

 spirited away on the breeze. This oblique turn is 

 well seen in the winged fruit of the ash (Fraxinus). 



