64 



BRITISH FERNS. 



attached on the concave side of the mass. The detached 

 pinnula on the left hand at the bottom of the cut shows the 

 veins, v^^ith the masses and their indusia in situ ; that on the right 

 hand shoves only the veins and the attachments of the thecse. In 

 approaching maturity the indusia are forced aside and ultimately 

 lost, the masses becoming circular, as represented in the detached 

 pinnula at the top of the cut, and often indeed confluent, 

 covering the entire under-surface of the pinnula. 



Professor Don, in the Transactions of the Linnean Society, 

 Vol. xvii. p. 436, observes, that "there are two very marked 

 varieties of this plant, the one with broader segments of a dark 

 green, and with the rachis of a pale purple hue ; the other, and 

 that the commonest, with the segments of 

 a more delicate texture, and the whole 

 frond of a pale green. The latter variety 

 varies much in size, according to soil and 

 situation ; in damp, shady places, it be- 

 comes the Filix-femina of English Botany, 

 and in more open exposed situations, the 

 irriguum ; but neither of these states is en- 

 titled to be regarded as a distinct form." In 

 these remarks. Professor Don has omitted 

 to mention a character which I think 

 of still more importance ; the variety, of 

 which " the segments are of a more 

 delicate texture," has the margins of each 

 pinnula folded together, and so convolute 

 as nearly to meet below, which character 

 causes each pinnula to look very narrow 

 from above : the pinnulae of the other 

 variety are spread out and flat ; the serra- 

 tures or lobes being perfectly displayed. 

 The Aspidium irriguum of Smith is a 

 variety of the convolute form ; it is not one 

 of those types of form which in P. aculeatum, L. dilatata, &c. are 

 constant in their peculiarity through a whole series of plants : 

 the characters given by Smith of " small size," " more lanceo- 

 late figure," " main stalk occasionally scaly and exactly qua- 

 drangular," "leaflets shorter, less linear, deeply serrated, or 

 partly pinnatifid," may correctly describe one frond, or one 

 plant, but they are not characters by which to distinguish any 

 type of form or series of plants ; and the name irriguum being 



