312 TKANSAGTIONS AND I'KOGEEDINGS OF THE [Sess. LXVII. 



On the genus Polystichum, Eoth (Aspidium, Swartz, 

 IN part), with special reference to p. angulare, Presl., 

 AND TO its Distribution in Scotland. By Alex. 

 Somerville, B.Sc, F.L.S. 



(Read 11th June 190P).) 



It is well to be reminded occasionally that our British 

 Ferns, including the Adder's-tongue and Moonwort, number 

 no more than forty-seven species, grouped into twenty 

 genera. 



Ferns are the most highly organised of cryptogamic 

 plants, and, by their elegance and grace, never fail to 

 command our admiration, whether we look at the humble 

 moss-like Hymcnophyllum or at the arborescent tree-fern of 

 Australasia, the Himalayas, and elsewhere. 



Though ferns are widely separated from flowering-plants 

 in the important respect that they do not develop nor are 

 reproduced by seeds, but, instead, by microscopic spores 

 filled with structureless protoplasm, they, on the other 

 hand, do claim kinship with phanerogams in possessing an 

 internal vascular structure of stem, of remarkable tough- 

 ness, which has, doubtless, much to do with the elegance of 

 their outward form. 



Fern foliage is strikingly varied, as may be gathered 

 from a sCirvey of our British species. This circumstance 

 helps not a little in classifying the various species. It is 

 not by the foliage, however, so much as by the varied 

 conditions and arrangement found in the fructification, 

 that ferns are grouped. Accordingly it is on inconspicuous 

 points that fern classification is mainly based, points which 

 are often more readily seen before the plant reaches 

 maturity, than when it is in the mature state. The points 

 of distinction require painstaking examination, and the 

 consequence is that the superficial student contents himself 

 with looking to external form, and there being, as it were, 

 two strings to the bow he has to use in determining his 

 plant, he, exercising his choice, selects the easier, and 

 succeeds fairly well. 



