154 THE MORPHOLOGY OF PTERIDOPHYTES 



also, that Mohria is the most advanced in its dermal 

 appendages, for they are glandular scales, whereas those of 

 the other three genera are hairs. In Anemia, only the two 

 lowermost pinnae are fertile. 



The prothalli are flat thalloid structures, except in Schizaea, 

 where they are filamentous, with occasional mycorrhizal 

 cells and with the gametangia at the tips of short lateral 

 filaments. Bower remarked that these filamentous prothalli 

 are 'the simplest prothalli known among the Pteridophyta. 

 They suggest a primitive state, and provoke comparison 

 with green Algae'. However, their simplicity is now regarded 

 as the result of evolutionary speciaHzation, instead of repre- 

 senting a primitive state. 



Of the four genera, Lygodium has the most complex 

 antheridial wall and the highest output of antherozoids 

 (156). 



Gleicheniaceae 



This family is represented by about 130 species belonging, 

 mostly, to the one genus, Gleichenia (some taxonomists 

 prefer to split the genus into four). A number of rather 

 different types of leaf morphology occur, two of which are 

 illustrated in Figs. 25C and 25D, but in all of them the growth 

 of the main rachis is arrested, until a pair of primary laterals 

 has formed. In some species, these are of limited growth 

 (Fig. 25C), but in others they too may terminate in dormant 

 buds, so producing a variety of patterns, some looking 

 superficially like a series of regular dichotomies (although, 

 in fact, they are psuedo-dichotomies, because of the dormant 

 apical bud in each angle). In others, there is a zig-zag 

 arrangement of branches (Fig. 25D). As in the Schizaeaceae, 

 therefore, the fronds are of indefinite growth, and some 

 attain a length of 7 m or more. They arise from a creeping 

 dichotomous rhizome which in most species is protosteHc. 

 A few, however, achieve a solenostelic condition, e.g. 

 G. pectinata, a relatively advanced condition which is associ- 



