[96 



GLEICHENIACEAE 



[CH. 



tufted hairs are found (Fig. 475). In Stromatopteris the dermal appendages 

 are very various, ranging from simple hairs to scales, and they may be 

 seated on emergences of various sizes. In Platyzoma there are only simple 

 hairs. In this it compares with G. linearis and pectinata. It will be seen later 

 how these divergent facts bear upon the phyletic comparison. 



The sori of the Gleicheniaceae are always superficial, being disposed in 

 a single row on either side of the midrib of the fertile segment. These 

 segments may be relatively long, with long rows of sori, as in the Dicra- 

 nopteris type (Fig. 476); or short and concave, so that there is space only for 



Fig- 47.S- Hairs from the base of the 

 leaf of Gleichenia pectinata. Each 

 is seated on a massive emergence, 

 from which it is easily detached, 

 the emergence remaining, as in 

 the Cyatheaceae. ( x 50.) 



Fig. 476. Gleichenia flabellata R. Br. 

 Midrib and three pinnules, showing 

 the arrangement and constitution 

 of the sori, with a variable number 

 of sporangia in each. 



few sori or even a single one, as in the Eii-GleicJienia type, and in Platyzoma, 

 and Stromatopteris. The sorus is as a rule typically radiate-uniseriate, the 

 sporangia being attached in a simple ring round a central receptacle. There 

 is no indusium. The number of the sporangia varies in different species, 

 2 to 5 or 6 being common numbers: but in the Cretaceous fossils from 

 Greenland Professor Seward found a larger number. 



Anatomy 

 The axis of those sporelings of Gleichenia which have been examined 

 contain a small protostele. In the great majority of species this structure is 

 maintained throughout life. But as the creeping rhizome increases the 

 protostele also enlarges, and finally settles down to a cylindrical form, of 

 approximately constant size, as it is seen to be in G. flabellata (Fig. 477). 

 There is a central core of xylem consisting in the adult of tracheides 

 interspersed with parenchymatous cells. Mesarch protoxylem-strands are 

 present near to the periphery, and those towards the upper side are con- 



