i88 MARSILEACEAE [CH. 



excepting Mohria, which appears to be an advanced xerophytic type, with 

 protective scales. 



(6, 7) The spore-bearing organs present the most exacting problem. 

 Where the sporocarp is solitary the origin, position, and lateral vascular 

 connections are sufficient evidence of its pinna-nature. The numerous 

 sporocarps all on one side of the petiole in M. polycarpa suggest a succession 

 of pinnae on an anadromic helicoid plan, such as is seen in the leaf of 

 Pteris se7)iipinnata (Vol. I, p, '^%, Fig. 82, C, D, E). Further, the branching 

 of the pedicels in M. quadrifolia (Fig. 459) has been referred on develop- 

 mental grounds to a production of pinnules, themselves developed as sporo- 

 carps (Johnson, I.e. p. 139). Accordingly the whole series of structures seen 

 in the Marsileaceae are referable in origin to parts of a normally branching 

 leaf, and the sporocarps may be regarded as pinnae or as pinnules (compare 

 Von Goebel, Organographies ii, 2, p. 1 1 36). Turning now to the SchizaeaceaC) 

 the spore-production in them is not limited to any definite part of the sporo- 

 phyll. In Mohria and Lygodium it is generally spread throughout its length: 

 in Anemia, though it is often restricted to the lowest pair of pinnae, this is 

 not constant for the genus (Goebel, Flora, Bd. 108, p. 319). In Schizaea it 

 is located on distal branchings of the dichotomising sporophyll. Thus the 

 variety seen in the Marsileaceae is matched by that in the Schizaeaceae: in 

 either family the fertile region may be whole pinnae or pinnules. 



The inner constitution of the sporocarp itself presents a further problem. 

 The alternate position of the elongated receptacles, and the superficial 

 origin of the sporangia facing on to the soral canals, which are surface- 

 involutions, are facts that suggest that the whole body is of the nature of a 

 condensed sporophyll, or rather part of it. Such a view involves fusion of 

 the parts together, and an additional tissue-development to produce what 

 is styled the "indusium." Lastly certain curvatures in the whole body will 

 demand consideration. Duncan Johnson remarks {I.e. p. 129) for Marsilea 

 that "there is never any curling in the extreme tip of the capsule suggesting 

 the circinate coiling of the leaf." He describes how the young sporocarp 

 "bends ventrally upon itself" But there is no mention of its rotation. 

 A natural structural indication of the orientation of the whole body when 

 mature is supplied by the outline of the vascular strand of the stalk, 

 especially at the point where it enters the sporocarp. A section through the 

 so-called "raphe" shows the vascular strand of the type of the Marsileaceae 

 and Schizaeaceae, orientated so as to suggest that the raphe is dorsal 

 (abaxial), and the sori ventral (adaxial) (Fig. 469, yi). To attain this position 

 there must have been some slight rotation, about | of a circle: this 

 will be clear from Fig. 469, B., C. In view of these points the hypothesis 

 seems to be tenable that the sporocarp consists of a rachis bearing two rows 

 of pinnules: this is indicated by the venation, for both families have con- 



