554 FILICALES 



arrested leaf-tip developing equally, and so strongly as to exceed the actual 

 apex which lies between them. But on the other hand, as the result of 

 comparison apparently of mature specimens, Tansley refers the leaf-architec- 

 ture ultimately to dichotomy. He states that "a bud normally arises from 

 the angle of the primary dichotomy." l In face of such diametrically opposite 

 statements the accurate observation of the ontogeny is most desirable; 

 hitherto the details of development of the Gleicheniaceous leaf have never 

 been worked out. 



The degrees of branching of the leaves have been made the basis of 

 subdivision of the genus into four sections (Fig. 308).- Goebel has described 

 the mode of protection of the resting bud seen in some species : the pinnules 



which stand nearest to the apex form protec- 

 tive scales, and they have been mistaken for 

 adventitious or aphleboid growths. 3 As a 

 matter of fact, the whole structure can be 

 referred to a normal pinnate development of 

 the leaf, altered by temporary arrest of the 

 apex, and by precocious development of 

 certain pinnae. Hairs and paleae are found 

 on the surface both of rhizome and leaf. 



The sori are always superficial, disposed 

 in a single row on either side of the midrib 

 of the fertile segment (Fig. 309). Typically 

 they are radiate-uniseriate, the sporangia 

 being attached in a ring round a central 

 receptacle : they are without indusium. The 

 number of sporangia varies in different 



Glcichcnicijlabellata, Br. Midrib and . 



three pinnules, showing the arrangement SpCClCS, tWO tO UVC being COmmOn numbers ; 



and constitution of the sori. with variable , .. 



number of sporangia. but the sorus may often be represented by 



a solitary sporangium (monangial sorus), 



especially towards the distal end of the segment, a fact pointing in the 

 direction of the Schizaeaceae : or the number may be larger than five 

 or six, as in G. pectiiiata and dichotoma (Fig. 310, -//), and this points in 

 the direction of the Cyatheaceae. 



The existence of the fossil Fern with fructification designated Oligocarpia 

 has been held as evidence of the existence of Gleicheniaceous Ferns as 

 early as the Palaeozoic period. But the fact that the Gleicheniaceous and 

 Marattiaceous sori are of the same type throws the burden of proof upon 

 the sporangia! structure, on which point it may be admitted that there is 

 some doubt. 4 But the Gleicheniaceous habit of frond is seen in the 

 Palaeozoic genus Diplotmema and other types, while certain Carboniferous 

 stems had an anatomical structure like that of the Gleicheniaceae. 5 But 



1 Ann. of Bo/., \\\., 1895, p. 479. - Diels, Nat. J'/faii\eii/'<u/i., i. 4, p. 352. 



3 Goebel, I.e., p. 318. 4 See below, p. 560. 



5 Scott, Studies, p. 263. 



