200 DORIS LOVE 



case on a quiet, warm day (Geiger, 1950). On the other hand, if there is a 

 high degree of turbulence in the air near the ground, even light seeds can 

 eventually be hfted to sufficient height for a long-distance dispersal to take 

 place (Ridley, 1930; Dahl, 1958). 



It seems that such seeds must have approximately the same properties as 

 loess or very fine sand, i.e. no diameter in any direction over 0.2 mm (Dahl, 

 1958), or a density of not more than 2.6 gr/cm^ with a largest diameter below 

 0.6 mm (J. Elson, Montreal, pers. comm.). Very few plant species have seeds 

 wliich come inside these narrow limits, and in our area only species of 

 Orchidaceae and certain Juncus, Sagina, Drosera, Pyrola, Phyllodoce, Loise- 

 leuria, and Harrimanella seem to qualify outright (cf. Table 6). 



Air turbulence is often created by thunderstorms in lower latitudes, but 

 the violent hurricanes in the North Atlantic area certainly create enough 

 turbulence in the ground layers of the atmosphere to move dust-seeds out of 

 their capsules and up to a sufficient altitude for long-distance dispersal 

 (cf. also Sverdrup, 1957). 



The quantity of spores (of ferns, clubmosses, horsetails, mosses, and 

 lichens, etc.) no doubt exceeds in relative amounts the mass of airborn 

 seeds, including dust-seeds (Ridley, 1930). Some must be regarded as ever- 

 present "air-plankton" (e.g. Lycoperdon, cf. Table 4, and Geiger, 1950), but 

 ecological and climatological factors certainly hmit the areas where both 

 spores and dust-seeds can develop into mature plants (SaHsbury, 1942). 

 Though some species of, for example, Orchidaceae, Lycopodium, Equisetum, 

 and various ferns reach very high latitudes, the bulk of them belong to more 

 southern areas. 



It cannot be denied, however, that there are a number of species which 

 could have [spread over our area very easily if the distances between the 

 landmasses at some time in the past were shorter than now (Love and Love, 

 1956; Dahl, 1958; Hadac, 1960). Under such circumstances it would be much 

 easier to account for the present distribution of species whose seeds are 

 carried moderate distances from the mother plant by the wind, and it would 

 explain, for instance, why we have a dominance of windspread species in the 

 western element of this flora (Dahl, 1958). The winds in the North Atlantic 

 are predominantly westerly, although occasionally easterly winds of carrying 

 capacity blow for short intervals (Orvig, Montreal, pers. comm.). 



But wind-dispersal does not consist only of material blown through the 

 air, it also includes heavier particles blown over the surface of the ground. It 

 is self-evident that open water limits this form of dispersal in most of our 

 area, but in the far north the continuous ice-cover over the Polar Sea might 

 provide means for ground dispersal of seeds over relatively long distances. 

 Thus, some Russian scientists (Tikhomirov, 1951; Aleksandrova, 1960) 

 believe that all the present flora of Novaya Zemlya has blown in from the 

 mainland over the Kara Sea and Strait in Post-glacial time. Whether this 



