STRUCTURE.] FILICALS. 95 



connected by cellular matter ; and the wood of those which 

 have arborescent trunks is formed by the cohesion of the 

 basis of such petioles round a hollow or solid cellular axis. 

 The organs of reproduction are produced from the back or 

 under side of the leaves. In Polypodiaceae, or what are more 

 commonly called dorsiferous ferns, they originate, either upon 

 the epidermis or from beneath it, in the form of spots, at the 

 junctions, margins, or extremities of the veins. As they 

 increase in growth they assume the appearance of small heaps 

 of granules, which heaps are called sort. If examined beneath 

 the microscope, these granules, commonly called sporangia, 

 theca, capsules, or conceptacles, are found to be little, brittle, 

 compressed bags formed of cellular membrane, partially sur- 

 rounded by a thickened longitudinal ring (gyrus, annulus, 

 gyroma], which sometimes at the vertex loses itself in the 

 cellularity of the membrane, and at the base tapers into a 

 little stalk. The sporangia burst with elasticity by aid of their 

 ring, and emit minute particles named spores or sporules, from 

 which new plants are produced : as from seeds, in vegetables 

 of a higher order. Interspersed with the sporangia are often 

 intermixed articulated hairs ; and, in those genera in which 

 the sporangia originate beneath the epidermis, the sori, when 

 mature, continue covered with the superincumbent portion 

 of the epidermis, which is then called the indusium or invo- 

 lucrum (membranula, Necker ; glandules squamosa, Guettard), 

 In Trichomanes and Hymenophyllum, the sporangia are seated 

 within the dilated cup-like extremities of the lobes of the 

 frond, and are attached to the vein which passes through 

 their axis, which is then called their receptacle. In Gleicheni- 

 acese, the sporangia have a transverse complete, instead of a 

 vertical incomplete, ring, and they are nearly destitute of 

 stalks ; in others the sori occupy the whole of the under sur- 

 face of the leaf, which becomes contracted, and wholly alters 

 its appearance : the sporangia have no ring, and the cellular 

 tissue of their membrane is not reticulated, but radiates 

 regularly from the apex. 



In these plants it has been in vain endeavoured to prove the 

 existence of organs of fecundation. Nevertheless, as it was 

 difficult for sexualists to believe that plants of so large a size 



