The Scottish Naturalist. 263 



seeds mature the hairs lengthen, and finally they become very 

 conspicuous, forming large heads like masses of silky cotton, 

 familiar to every one that has seen a Highland moor in summer. 

 When the seed-like carpel breaks away the hairs are carried with 

 it, and the whole floats away on the breeze. 



The corolla or inner floral envelope is so seldom modified 

 apart from the outer that it needs no further comment here. 



In several of our native plants the flower-stalk bears hairs 

 which elongate after the seeds are fertilised, and at last form 

 relatively large tufts. Among the grasses Phragmites communis 

 (reed) and Arena pubescens may be instanced. Typha lat-ifolia 

 also shows this arrangement. In such cases the flower-stalk 

 breaks away, remaining attached to the ripe fruit. 



The lime-tree or linden (Ti/ia) gives an excellent example of 

 the bract forming the wing. The flower-stalk (bearing several 

 flowers, and therefore also several fruits) is adherent in part of 

 its length to the long rather narrow bract. When the seeds are 

 ripe the bract falls off with the fruits and flower-stalk, and is a 

 very efficient means of conveying them to some distance before 

 reaching the ground. In the hornbeam (Carpinus) and hop 

 each fruit stands sessile in the axil of a small bract which falls 

 off Avith it like a wing. In many grasses the glumes or bracts 

 fall off with the fruit, and form imperfect floats — e.g., in Holcus, 

 Plialaris, &c. 



Yet other modifications adapted for this mode of conveyance 

 of seeds are met with, but it would be tedious to dwell on them 

 now; and, moreover, they rarely are found in Scottish plants. 



Conveyance by water is a far less general means than by wind, 

 and special adaptations are rare. Of course, the seeds or fruits 

 of any plants growing on the side of a stream may fall into it, 

 and may be conveyed to a considerable distance, if light enough 

 to float, before being again cast on land. Of this mode of con- 

 veyance we have clear proof in the occurrence of typically alpine 

 plants frequently here and there along our rivers in the lower 

 grounds. But no special adaptations are needed or are met 

 with for this method. Very few of our native plants live float- 

 ing freely on the surface of the water, though in the tropics such 

 plants are so abundant as to form floating islands, often over 

 an acre in extent. The seeds of these plants germinate under 

 water, and they are dispersed without special means by the 

 movements of the plant freely on the surface of the water, 

 carried along by winds or by currents. 



