2i6 GLEICHENIACEAE [CH. 



(Fig. 475). It is but a slight step structurally from this to the scales seen 

 in many species, including not only the 

 xerophytic Eu-Gleichenia, but also repre- 

 sentatives of the less specialised section 

 Dicranopteris. For instance in G.flabellata 

 the scales have a peltate insertion upon the 

 stalk, with short bristles radiating from the 

 margin and base, suggesting an origin from 

 some branched hairs such as those of G. 

 pectinata by broadening the basal region 

 of the main bristle (Fig. 495). In this 

 Family the dermal appendages do not 

 greatly help the phyletic argument: for 

 though G. pectinata and linearis appear to 

 be relatively primitive in respect of their 

 dermal appendages they are advanced in 



their anatomy, and in their soral characters. 



-r> ^ •- • r i. • i-i i- J Fig. 40^. Flattened scale, with stift' mar- 



But It IS a frequent experience that advance |„tf ^pi^es, from the i^izome of Glei- 



does not necessarily march parallel in all cheniaflabdlata. (xcjo.) 



features compared, and this appears to hold for these two species: for though 



advanced sorally they bear appendages of more primitive type (see 



Studies II, ^;^;^. of Bot. xxvi, p. 272). 



The position and structure of the sorus of the Gleicheniaceae compares 

 on the one hand with those of Marattiaceae and of Todea, and on the other 

 with that of the Cyatheaceae and Matonineae. The absence of all indusial 

 structures is a significant fact for comparison on the one hand with the 

 Osmundaceae and other Simplices, on the other with the simpler Cyatheoid 

 Ferns. It contrasts broadly with the presence of indusial growths in certain 

 Schizaeoids and Dicksonioids. The departure of the sorus in G. linearis 

 2ir\d pectijiata from the uniseriate type characteristic of most Gleicheniaceae 

 and of all the Marattiaceae is an important fact. It appears in species with- 

 out scales, but one of them is advanced anatomically to full solenostely in 

 the adult state, though the ontogeny shows how this emerges from protostely, 

 and suggests a phyletic origin of this more advanced state. The same two 

 species bridge over also an important step in sporangial structure. The 

 details have been described above, but the net result appears in the spore- 

 output per sporangium, which amounts in G.flabellata to numbers comparable 

 only with those of Eusporangiate Ferns: G. pectinata and Eu-GleicJienia 

 appear to take a middle position in the family, while G. linearis has the 

 smallest output per sporangium, thus leading towards that relatively small 

 number characteristic of the Leptosporangiate Ferns. The low output goes 

 along with a larger number of sporangia in the sorus. Such features clearly 



