LOXSOMACEAE 



573 



The receptacle performs an important part in connection with dispersal. 

 At first it is short, so that the sporangia are all included within the indusium 

 '(Fig. 320 E), and this is so till the oldest sporangia are mature; an inter- 

 calary growth then takes place at the base of the receptacle, the thin- 

 walled cells above the terminal mass of tracheids (tr.) become greatly 

 elongated (Fig. 320 A), forming a sort of pseudopodium (ps.\ upon which 

 the sporangia are raised so as to project beyond the lip of the protective 

 indusium, and are thus free to scatter their spores. The arrangement is 

 -similar to that seen in the Hymenophyllaceae, but in Loxsoma the pseudo- 

 podium is formed independently of the long-continued formation of a 

 series of sporangia. 



The sporangium makes its first appearance as a massive deeply sunk 

 cell, near the base of the groove between the receptacle (r) and the 

 indusium (ind.) (Fig. 320 B) : the first segmentation in it passes down to 

 the base of the cell, as in the Schizaeaceae and some other Simplices ; the 

 later ones cut the previous wall obliquely, and thus a three-angled conical 

 cell is surrounded by three lateral segments. The cap-division, and 

 segmentations forming the tapetum take place in the usual way ; the inner 

 series of tapetal cells enlarge considerably, and become polynucleate, thus 

 resembling other large sporangial types. The definite sporogenous group is 

 composed of 16 spore-mother-cells, which undergo a tetrad division to give 

 typically 64 large spores. 



ANATOMY. 1 



The chief point of anatomical interest is the structure of the stele of 

 the stem : a transverse section of an internode shows a typical solenostele, 

 with phloem, pericycle, and 

 ^ndodermis, both outside 

 and inside of the continu- 

 ous ring of xylem. The 

 protoxylem elements are all 

 scalariform, and are not 

 localised into groups, but 

 -are distributed around the 

 periphery of the solenostele. 

 Where a leaf-trace is given 

 off the tube of the stele 

 opens, forming a foliar gap 

 on the acroscopic side. 

 The leaf-trace itself consists 

 of a single vascular strand, 

 showing the horse-shoe outline in transverse section (Fig. 321). An unusual 

 feature is the occurrence of islets of parenchyma in the sclerenchymatous 

 masses of the stem, a peculiarity shared with certain species of Dicksonia. 



FIG. 321. 



Loxsoma Cunninghami. Diagram showing the form of the 

 vascular system at the node of the rhizome. jj = solenostele ; lt = 

 departing 1 eaf- trace : lg = leaf-gap. The arrow points toward the 

 apex of the rhizome. (After Gwynne-Vaughan.) 



Gwynne-Vaughan, Ann. of Bot., vol. xv., p. 71. 



