632 MR JOHN M'LEAN THOMPSON ON 



Dearly allied to Gleichenia." F. Muller, however, rejected the opinion expressed 

 in the Synopsis Filicum, and maintained that Platyzoma should be considered a 

 species of Gleichenia; accordingly, he named it Gleichenia 'platyzoma. In 1878, 

 Benthem endorsed the opinion of Hooker and Baker, and, writing in Flora 

 Australiensis, vol. vii, p. 696, he held that Platyzoma " is a genus limited to the 

 single species endemic in Australia. The great difference in ' fructification ' as 

 well as in habit appears to preclude its union with Gleichenia as proposed by 

 F. Muller." In 1897, H. Christ* sank Platyzoma in Gleichenia, and named 

 it Gleichenia microphylla, while in 1902 Diels t followed a similar course. And 

 lastly, in 1906, Carl Christensen, in his Index Filicum, placed Platyzoma in very 

 close relationship to Gleichenia, but at the same time was not disposed to reduce 

 Platyzoma to the rank of a species of Gleichenia. It will be noted, then, that 

 the systematists, without exception, have followed Brown's example in placing 

 Platyzoma in the Gleicheniacese, and that the only point upon which opinions 

 have differed is the rank which Platyzoma merits within this group. 



The following characters of Platyzoma have been recorded by the systematists : — 

 The axis is a short, horizontal rhizome beset with a thick covering of long, 

 glistening, golden-brown hairs. The branching and fibrous roots spring from 

 the lower surface, and occasionally from the sides of the stem. Regarding the 

 heterophylly there is but a single statement, namely, that which is found in 

 Brown's original description of Platyzoma. It is remarkable that later systematists 

 have not even referred to Brown's remarks on this feature, for he stated clearly 

 that Platyzoma possesses not only undivided pinnate leaves, but also leaves of 

 a compressed and filiform character. The pinnate leaves range from about 6 

 inches to 1 foot in length. They are densely crowded upon the upper surface and 

 sides of the rhizome ; they are dark and sclerotic, and their bases are surrounded 

 by clumps of firm hairs. They are simply-pinnate and unbranched, and both 

 petiole and rachis are smooth and slender. The pinnae are small and numerous, 

 and seldom exceed 2 mm. in length. They are ovate-orbicular in outline, and 

 their margins are so revolute that the stomata — which are restricted to the 

 lower surface — are in a nearly closed cavity. The upper epidermis is smooth 

 and strongly cuticularised, and much of the mesophyll is composed of water- 

 storage tissue. The margins of the pinnae bear numerous minute irregular hairs, 

 and similar hairs are distributed upon the lower surfaces of the pinnae. The 

 venation is a short sympodium. There are but a few sporangia in any fertile 

 pinna. They are disposed terminally upon the lateral branches of the sympodium, 

 and are at maturity globular and almost sessile. They are hidden beneath the 

 broad revolute margin of the pinna ; they are irregular in form, and their dehiscence 

 is variable. 



IJkxthem has noted (loc. cit.) the localities from which Platyzoma has been 



* Die Famkraiiter der Krde, p, 339. f Eng. and Prl., i, 4, p. 355. 



