XXII] . SPORE-PRODUCING MEMBERS 163 



a fact that accords with their primitive position, and the near relation of 

 their leaf-architecture to simple dichotomy. 



The dermal appendages are simple hairs in Lygodium, Schizaea, and 

 Anemia, sometimes with glandular terminal cells. But in Mokria, which is 

 distinguished by advanced dictyostely, by a type of leaf which corresponds 

 to that seen in many advanced Leptosporangiates, and by a relatively low 

 spore-output from each sporangium, the hairs are replaced by broad scales, 

 each with a distal glandular cell. This state may have been developed in 

 relation to its dry habitat: but it is significant that the more advanced 

 structure of the scale goes along with an advanced state in respect of other 

 features also, 



Spore-Producing Members 



In the Schizaeaceae the sporangia are solitary. Prantl recognised each 

 of them as constituting a "monangial sorus." The purist may regard this 

 as a contradiction in terms : to the student of F'ern-phyletics it suggests a 

 primitive state reminiscent of the single distal sporangium, as in Botrychium 

 or Stauropteris (Vol. I, p. 208). Prantl accurately worked out the develop- 

 ment in all the living genera, and found the sporangia to arise in acropetal 

 order on each fertile segment. He ascribes to them an origin from cells of 

 the marginal series, each with a terminal position on a fertile vein. In fact, 

 the position is that which would naturally follow as a consequence of the 

 webbing of the segments w^hich the study of leaf-architecture discloses, so 

 as to form a flat leaf-expanse. Doubt has been cast upon the correctness 

 of Prantl's facts by Diels {^Nat. Pflansenfam. i, 4, p. 360): but more recently 

 all the genera have been re-examined, with the result that Prantl's observa- 

 tions have been upheld {^Lygodium, Binford, Bot. Gaz. xliv, p. 214; see Vol. I, 

 Fig. 235: Schizaea,^o\N&x,Ann. of Bot. xxxii, p. i, 1918: Anemia, Stevens, 

 Ann. of Bot. xxv, p. 1059: Mo/iria, ^owqy, Ann.of Bot. xxxii, p. 9). A con- 

 sequence that follows will be that the indusial protecting flanges or flaps, 

 which differ in detail in the four genera, all appear as accessory surface- 

 growths of the supporting leaf-segment. They arise simultaneously with, or 

 subsequent to, the sporangia which they protect: but growing strongly they 

 force the marginal sporangia into an apparently superficial position. A 

 knowledge of the development is therefore essential for the proper under- 

 standing of the morphology of the sporophyll. 



The fertile segments of Lygodium appear as strobiloid terminals to the 

 sterile region of the leaf (Figs. 438, B, and 44.1, B, C). Each solitary sporan- 

 gium is enveloped in a sort of pocket formed on the upper side by what 

 appears to be part of the surface of the blade, on the lower by a membranous 

 flap. It is seated near to the end of a vein which, passing beneath its stalk, 

 terminates in a minute tooth at the margin of the pinnule (Fig. 441, C). 



