10 64 Proceedings of the Royal Irish Academy. 



can be effectually carried out (see infra). In another section of the present 

 paper (pp. 72-80) are given the results of some experiments made to 

 determine the relative efficiency for dispersal of the seeds of some British 

 pliers. 



Seeds which are capable of wide dissemination by wind are found in many 

 different natural orders, and in plants of very varying stature, and of a wide 

 range of hahitat. They occur in forest trees, and in herbs only a few inches 

 in height : in plants which grow in dry ground and in water ; on mountains 

 and on plains. The seeds owe their effectiveness for dispersal to a variety of 

 causes. In the British flora the most conspicuous group of wind-borne 

 seeds is found in the Compositae, and mostly among the thistle group. Here 

 dispersability is due to the feathery shuttlecock-like pappus — the modified 

 calyx-limb — which crowns the seed. Feathery appendages of a simpler nature' 

 which act in the same way, are found in plants of various other orders — for 

 instance, in the Pasque-flower (Banuneulaceae), the Hare's-foot Trefoil 

 (I^gnininosae), the Mountain Avens (Bosaeeae), the various Willow-herbs 

 (Onagraceae), and so on. A membranous or coriaceous wing, regularly or 

 irregularly disposed around the seed, is also sometimes effective, as in the 

 Elm tTrticaceae), Ash (Oleaeeae), Scotch Fir (Coniferae), or Cow-Parsnep 

 (Umbelliferae). Or again, the very small size and lightness of seeds may 

 promote dispersal, as in the case of the Orchids, Bushes, and Broom-rapes ; 

 though, as shown below, reduction of size is in the Bhaneroganis not carried 

 far enough to render this device very efficient, as it is in the Cryptogams. 



The seeds which possess characters rendering them specially capable of 

 being dispersed by the wind may be classed as 



1. Plume seeds. 



2. Wing seeds. 



3. Powder seeds. 1 



While no doubt can exist as to the efficacy of plumed and winged seeds 

 for conveying the coming generation well beyond the influence of the parent 

 plant — especially when these seeds are borne at some height above the 

 ground — the tendency of the majority of recent writers is to discount their 

 efficacy in long-distance dispersal. To quote a few observations and 

 opinions : — 



Over half a century ago, before Darwin's and Wallace's advocacy of long- 



1 A more minute classification, with eiamples, of wind- dispersed seeds will be found in 

 G. E. Mattei: Aeronautiea Vegetabile. Boll. orto. bot. nniv. Xapoli, i, fasc. 3, pp. 311-331 

 (figures), 1902. (Abstract in Bot. Jahresbericht, xrxii, abt. 2, p. 491). Also in P. Vogler 

 Uber die Verbreilungsmittel der schweizerischen Alpenpflanzen . Flora, lxxxix, pp. 1-137. 1901. 



