eS TRANSACTIONS, NATURAL HISTORY SOCIETV OF GLASGOW. 



spores embedded in ice, as Lyell has shown, must 

 sometimes be floated far away from their place of 

 origin. The presence of arctic species in certain 

 localities can thus be accounted for. As the Glacial 

 Period drew to a close, many northern plants must 

 have been distributed in this manner. The carriage 

 of seeds by ice can, however, be only an occasional 

 occurrence, and, though important in relation to the 

 geographical distribution of plants, possesses only a 

 secondary interest from the point of view of 

 botanical biology. 



5. Wind Transport. — No natural agency is more 

 taken advantage of by plants for the dispersion of 

 their germs than the wind. A large percentage of 

 the floating matter of the air is of organic origin. 

 This fine organic dust must consist partly of vege- 

 table cells capable of development if they should 

 happen to alight in a favourable soil. In the case 

 of minute unicellular plants, such as Bacteria and 

 Micrococcus, the entire organism may remain sus- 

 pended in the air for a length of time and be 

 carried hither and thither by air currents. Strong 

 winds which uproot large plants may also occasion- 

 ally transport them short distances. But it is only 

 with the reproductive bodies thus blown about that 

 we have now to do. 



As a dispersive agent for securing widespread 

 and general distribution, the wind possesses great 

 efficiency. Wind - dispersion, however, generally 

 mvolves a large amount of waste. Especially is this 

 true in the case of pollen-grains, where the trans- 

 ported bodies require not only to be distributed, but 

 to be delivered at particular spots. For this reason 

 more economical modes of convej'^ance are frequently 

 adopted. And even in those plants which employ the 

 wind, we often find special arrangements for re- 

 stricting the waste and securing the proper delivery 

 of their germs, 



(ft) Spores. — Among the Cryptogams, wind-dispersion 

 is very general. The spores of Ferns, Lycopods, Mosses, 



