312 



Forniation and Flora of a Shingle Island. [Sess. 



The number 13 as regards wind would doubtless be an 

 underestimate, since the 1 3 are all obvious cases ; and there 

 must be many cases in which the wind plays an appreciable 

 though subordinate part. If we suppose the wind to have 

 been a factor in 41 cases — that is, in all except those which 

 were obviously due to water - carrying — we have as " total 

 weight of factor" 53, which is probably nearer the truth. 



Making allowance for the difficulty of arriving at anything 

 approaching exactness, we think it is pretty clear that the 

 river, and " close proximity," are the most important factors, 

 and that there is little to choose between them ; that the wind 

 comes next in importance ; and that the mere profusion of a 

 species in the neighbourhood, unless in closest proximity, goes 

 for comparatively little. As regards dispersal by wind, we 

 may note that the plants growing in the fields would not have 

 such a good chance as those growing in the riparian strip. In 

 the fields, any seeds (except those of certain composites, &c., 

 specially adapted for wind dispersal) would, on becoming 

 detached, at once fall and be buried in the thick vegetation ; 

 whereas in the stony or sandy patches of the riparian strip, 

 seeds would have a better chance of being blown to a 

 distance. 



1 " A factor " is indicated in our list by x ; " an important factor "by x x ; 

 and " the chief factor "by " x x " when this mark is found in only 1 out of the 

 4 possible columns. 



■^ It will be seen that we have assigned a value of 1 for every case of a probable 

 factor, 2 for an important factor, and 3 for a chief factor ; having counted im- 

 portant factors twice (as " factors " and as "important factors"); and counted 

 " chief factors " thrice (as "factors," "important factors," and "chief factors "). 

 This seemed to us a fair way of arriving at the "total weight" of a factor. 



