49 



ASPLENIUM ADIANTUM-NIGRUM. Black Spleenwort. TAB. XXVIII. 



Fronds triangular attenuated or ovate, twice or thrice pinnate : 

 pinnae triangular : pinnules ovate or ovate-lanceolate, inciso-pin- 

 natifid, sharply toothed. Sori linear-elongate, approximate to the 

 midvein. 



Asplenium Adiantum-nigrum, Linrueus. E. B. 1950. Generally 

 adopted. 



One of the most generally distributed, of our smaller ferns, being 

 found in almost every part of the kingdom, growing in the crevices 

 of rocks and old walls and on shaded hedge-banks. The fronds 

 spring in tufts from the crowns of a slowly-branching rhizoma, 

 and vary greatly in development in different habitats, being often 

 on exposed walls and rocks not above two or three inches in length, 

 while under the influence of shade and moisture they extend to one 

 or two feet. The rachis is bare about half of its length, and this 

 part is glossy and of a deep purple almost black. The leafy portion 

 of the frond is mostly of an elongated triangular outline, but 

 sometimes perfectly deltoid, the lowest pair of pinnae being always 

 longer than the others, unless occasionally in very small specimens 

 when an ovate-lanceolate form prevails. The pinnae are pinnate, 

 obliquely triangular, and generally point upwards toward the apex 

 of the frond ; they differ much in division, but it is only in very 

 large fronds that the tripinnate character is fully developed. The 

 ultimate divisions are unequally toothed, the teeth being more or 

 less attenuated or obtuse, but always terminating in a point. The 

 venation is very distinct, and varies with the division of the frond, 

 the fructification being always produced on the inner or upper side, 

 near the separation of the branches from the midvein, and thus 

 occupying the middle of the pinnules. The sori are linear, covered 

 at their first appearance with a white indusium attached on the 

 outer side to the vein ; in maturity this is covered by the expansion 

 of the thecse and the sori become confluent, often spreading so as 

 to occupy the whole under surface. 



The protean character of this fern is apt to mislead the too 

 sanguine collector in his search for novelties, and an assemblage 

 of all its diversities of form would certainly puzzle the discrimina- 

 tive faculties of any one beholding them for the first time : a little 

 farther acquaintance, however, and especially the results obtained 

 by cultivating them under corresponding treatment, will soon 

 dispel any illusion regarding specific distinction. A very striking 

 difference is presented in contrasting the two extremes of form to 

 which it is liable, the intermediate and most common one being 

 that on which the foregoing description has been chiefly framed. 



