33 



though the bipinnate character is tolerably constant in full-sized 

 plants, the pinnae are rather lobed or pinnatifid than pinnate in 

 those of smaller size, and this difference is often independent of 

 age. The first upper division at the base of each pinna, whether 

 lobe or pinnule, is always larger than the others, and, standing 

 parallel with the main rachis, the two series thus formed present a 

 very peculiar appearance in the general aspect of the frond, espe- 

 cially of the upper face. All of the principal divisions terminate 

 in a sharp spinous process, and are more or less fringed on the 

 margin with spiny serratures. The rachis is leafy to within a few 

 inches of its base, and is clothed throughout with reddish-brown 

 or rust-coloured scales, which are broad and densely crowded below, 

 but become gradually fewer and more attenuated towards the 

 extremity of the frond. There is nothing peculiar in the fruc- 

 tification, beyond the regularity of the disposition of the sori, 

 and their occurrence almost exclusively on the upper pinnae only ; 

 they are generally rather large in proportion, and often become 

 confluent. 



A fern liable to assume such diversity in outline and division as 

 this, could scarcely fail of becoming a subject of contention among 

 botanists, relative to the individual claim of its more permanent 

 varieties to the rank of species. To enter into any minute detail 

 of the differences presented by the so-called species of Polystichum, 

 as figured or described by past writers, would be to little purp.ose ; 

 it will be sufficient here to remark that three apparent forms of 

 the plant now before us have been so distinguished, and named 

 respectively lobatum, aculeatum, and angulare. The first two are now 

 universally admitted to be merely different states of the same plant, 

 dependent on age or other circumstances ; the last occupies, though 

 somewhat equivocally, a more decided position as a separate species, 

 in the works of the most recent botanists ; that position I will 

 leave it, but rather that its prominence may lead to farther inquiry, 

 than from any conviction of its being other than a false one : loba- 

 tum and angulare, indeed, appear to me the extremes of a series 

 connected by so many intermediate modifications of form and 

 habit, that, in the absence of more important differential fea- 

 tures than have hitherto been established, it is utterly impossible 

 to determine the limits of either. As varieties, the three may be 

 thus defined : 



1. lobatum. Frond rigid, simply pinnate : pinna lobed or pin- 

 natifid. TAB. XVI. 



2. aculeatum. Frond rigid, sub-bipinnate : pinnules more or 

 less decurrent. TAB. XVII. 



3. angulare. - Frond lax, bipinnate : pinnules distinctly stalked. 



Under all its varieties of form, Polystichum aculeatum is among 



