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PLUMOSE VARIATION IN FERNS.* 



As the plumose or extra feathery varieties of Ferns are 

 universally recognised as the most beautiful, since being 

 purely extensions of normal growth, they are not open to the 

 objection sometimes raised that other forms of variation are 

 " monstrous," a little consideration of their nature may not 

 be out of place. As a typical form we may take the so- 

 called Welsh Polypody [Polypodium viilgare camhvicum), a 

 very old variety. The normal frond of the species consists 

 of a stalk flanked on either side by a series of smooth -edged 

 somewhat blunt-ended lobes, about one-third inch wide, 

 and on robust plants one and a-half inches long, the stalk 

 forming roughly one-third of the frond length. At the 

 back of these lobes there are bright yellow spore heaps, 

 round, and of exceptionally large size, and the spores them- 

 selves are yellow, and also much larger than those of most 

 ferns. In the Welsh Polypody, however, we find a very 

 different formation, the normal smooth-edged narrow lobes 

 or pinnae are transformed into deeply cut wide ones with 

 long pointed segments, an inch long or more, set closely 

 together, with the result that these pinnae overlap, and as 

 they are also longer than the normal the frond is very much 

 wider and, indeed, has no resemblance at all to the normal 

 species, even the texture being thin and papery. Another 

 difference is that spores never appear, the fronds are invari- 

 ably barren and it is this feature, conjoined with the extra 

 foliose character, which distinguishes the true plumosums 

 of all s[)ecies. It would appear that it is this absence of 

 spore producing capacity which determines the extra leafy 

 development, for if we examine the veins of P. vnlgave 

 normal we find that a certain number of them, starting from 

 the midrib, stop abruptly half-way across, and at this point 

 serve to form and feed a spore heap, and this, like all repro- 

 ductive action, concentrates in itself a large amount of vital 

 energy. In P. v. camhvictun most of the veins continue, and 

 the few of them which stop half way produce no sorus but 



•■- By permission of the Gardeners' Magazine. 



