ig. 590. Median section of a 



18 DAVALLIOID FERNS [cn. 



receptacle lying at the base of the pocket produces a mixed sequence of 

 closely packed sporangia. When mature their stalks are greatly elongated, 

 so as to lift the ripe capsules above the level of their fellows, and thus to 

 secure the discharge of the spores. 



The origin of the sorus has been examined by Von Goebel in Davallia 

 dissecta {Organographie, p. 1 143, Fig. 1 134). My own observations were made 

 on D. pentapJiylla Bl., a species in which the mature 

 sori are distinctly intra-marginal (Fig. 588,/). The 

 question is whether or not the receptacle is truly 

 marginal in the first instance in such species. First 

 the leaf-margin becomes flattened, and the indusial 

 flaps arise as superficial growths back from the 

 flattened margin. The lower (/) (Fig. 590) takes 

 precedence at first: but the more massive upper 

 indusium (2^), which is later assimilated to the general 

 leaf-surface, extends by intercalary growth, and 

 overtops it. Meanwhile sporangia appear upon the 

 flattened receptacle between them. Thus the sorus young 'sorus of D. peutaphylia 



7^ IT ■ r • 1 • • 1.1 u -i. Kl. The lower indusium (/) has 



m Davallia is of marginal origin even though it run out into a single layer of cells, 

 may appear superficial when mature. The more or the upper {u), which ultimately 



. . . Ill I forms the false margin of the leaf, 



less marginal position of the adult depends upon is more bulky, and shows signs 

 the varying activity of intercalary growth in the of intercalary activity. The first 



-' ° •' •' ° sporangium occupies a central 



upper indusium. The further development of the position on the receptacle, and 



1 1 rn i-7~i //■ -jr^j ■ tti a later one is seen between it and 



sorush^shQen M\o\\&d\nDavalhagriffithiaiial\k.; ^j^^ ^^pp^, ^^^^ ^^^,^ indicating 

 here the receptacle remains flat, and the earliest a gradate sequence. (X250.) 

 sporangia arise median upon it, thus again suggesting a gradate sequence; 

 but soon the sorus becomes mixed, successive sporangia being initiated 

 promiscuously over the whole surface, pushing their way upwards between 

 the long thin stalks of those already present. The sporangia themselves have 

 the structure usual in advanced Leptosporangiate Ferns, with a vertical 

 annulus of relatively few cells, and stalks composed, in part at least, of only 

 a single row of cells (Fig. 591). 



The facts thus detailed for Davallia indicate it as an advanced type in 

 a sequence derived from a Dicksonioid source with marginal sori. The 

 individuality of the sorus is maintained throughout the genus; the habit 

 remains fairly stable in these creeping F'erns, with their much-divided 

 leaves and open venation. While the typical Dicksonioid Ferns have pre- 

 valent solenostely usually with an undivided leaf-trace, hairs as dermal 

 appendages, and marginal sori of the gradate type with conical receptacle, 

 slightly unequal indusial lips, and massive often short-stalked sporangia; in 

 Davallia we see an advanced state of disintegration of the vascular system, 

 though clearly referable to a solenostelic origin, scales as dermal appendages, 



