2 60 The Scottish Naturalist. 



conveyed, as pointed out by Darwin, on the feet of 

 wading birds to considerable distances. But in this 

 case there are no special adaptations of structure neces- 

 sary, so there is no need to refer to them at greater 

 length. 



4. In some plants the seeds are thrown to some distance 



by elastic dehiscence of the seed-vessel, — e.g., in the 

 broom, or of a seed-coat, as in the wood-sorrel. 



5. Movements may be effected by awns. 



Wind as an agent in dispersion. — One of the simplest and 

 most general modes of utilising wind as an agent is seen in 

 plants which bear the fruits supported on a stalk of some 

 length — e.g., foxglove, poppy, hemlock, and many others. In 

 most of such plants the fruit is dry, and splits open in someway 

 or other to allow the escape of the seeds, which in such fruits 

 are generally numerous and small. In these fruits the opening 

 is almost always near the top ; or if, as in the bluebell {Cam- 

 panula), it is near the base, the fruit usually hangs reversed. 

 In this way the seeds are retained in it so long as it is at 

 rest, but when the fruits and stems are driven about by wind 

 the seeds are thrown to some distance around. In some plants, 

 such as the hemlock, the fruits are one-seeded, and do not split 

 open, but remain attached when ripe, till jerked off when the 

 plant is shaken by wind. Seeds of small size are carried off 

 in the air, and are blown about like so much dust ; and among 

 cryptogams this is a very frequent mode of distribution, and 

 the geographical range of these plants is often extremely wide. 

 Among phanerogams or flowering plants the seeds are seldom 

 small enough for this, but they are frequently rendered suffi- 

 ciently light by modifications of various kinds ; — in their own 

 structure if set free from the seed-vessel, or in the carpel or 

 outer parts of the flower in the case of one-seeded indehiscent 

 carpels. 



In orchids generally, and here and there among other plants 

 (e.g., Pyrola, Parnassia, Drosera angliea, &c), the seeds are 

 very numerous and small, and the outer coat of the seed much 

 wider than the inner, forming a loose bag filled only with air ; 

 hence such seeds are very light and are easily blown about. 



A number of plants have the outer coat of the seed prolonged 

 to form a thin, membranous wing, yielding the same advantage. 

 In some (e.g., Spergularia marginata and Rhinanthus crista- 

 galli), the wing surrounds the seed. No native Scottish plant 



