ADIANTUM. 



241 



(several times subdivided) ; they are generally smooth and vary in length 

 from 6in. to as many feet. Another distinctive character, almost peculiar 

 to all members of the genus, is found in the nature of the veins of the 

 pinnge, for they are simple, radiating (all starting from a common point), and 

 forked ; but except casually in A. lucidum, A. macrophyllum,, and perhaps 

 some other species, they are anastomosing (running into one another) only 

 in four known species, which are termed ITewardia, J. Smith. The Capillus- 

 Veneris Group has flabellato-cuneate segments (sub -divisions fan-shaped or 

 rounded at the top and wedge-shaped at the base) ; but even these leaflets are 

 still without distinct midrib, whilst a few species have segments equilateral 

 (equal on all sides), and in habit somewhat resemble species of Pteris 

 and Schizoloma. In all Adiantums the sori (masses of spore cases) are 

 disposed on the edge of the pinna?, either in a continuous line or 

 interrupted, and vary in shape, being sometimes kidney -shaped, elliptical, 

 round, or even linear (much longer than broad) : they are usually 

 numerous and distinct, although there are exceptions. In all cases also the 

 involucre, or indusium (outside covering), which is formed of a reflexed 

 depression, is of the same shape as the sorus (heap of spore cases), which 

 it covers, and varies in form according as the margin of the frond is 

 more or less either dented or entire. This outside covering, which acts 

 as a protection to the spores, after a time becomes replicate (doubled down), 

 so that its upper part, which bears the capsules, comes in immediate contact 

 with its lower part. 



As regards the variety of forms, the genus may be considered very rich, 

 for every one of the known Adiantums finds its place in one of the eight 

 following groups, into which the whole genus is subdivided : 



1. — A small group of species with simple (undivided) fronds, of which 

 A. reniforme is the type. 



2. — Eadicantes (Ra-di-can'-tes), or " Rooting Group," in which the 

 fronds are always simply pinnate (never divided to the midrib more than 

 once), and the midrib is often elongated and takes root at its apex, where a 

 new plant in all respects similar to the parent is thus produced. A. caudatum 

 may be given as a typical subject. 



3. — Polysorous (Pol-ys-or'-ous), or " Many -sori -bearing Group," com- 

 posed of species with fronds once or more pinnate, the fruit disposed in 



2 i 



