KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 63. N:0 8- 



31 



larger ones new sporophylls arise, and this process may become repeated, resulting in 

 a dense tuft of leaflets (fig. 10 e). Transitions between proper sporophylls and fertile 

 segments of the frond, each witli an apical sorus, are not uncommon. The average size 

 of the sporophylls is 4 — 5 x 3 mm. The sori occupy the surface on both sides, leaving 

 a narrow sterile brim. The formation of the tetraspores does not offer anything very 

 particular; se fig. 11 c — d. 



Apical groivth. This must be examined on the minute proliferations, as the rapid 

 formation of cortex very quickly obscures the view. A young leaflet is seen in fig. 12 a. 

 It is built after the scheme of Delesseria, but as yet no top-cells of 3. order are developed; 



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Fig. 12. Microrhinus carnosus: a — b small proliferations, showing growth niodus; C older apex; d cross section of lamina 

 near margin, e of old stipe; a — d X 240, e X 70. — Cortex cells dotted. 



these are visible in fig. 12 b, a somewhat låter stage, where the formation of cortex has 

 already begun. Such top-cells do not, as far as I can see, ever become active, the cells 

 of the central filament do not get much elongated, so that little space is left for the de- 

 velopment of branches of 2. order. Fig. 12 c shows an older apex. 



Formation oj cortex and anatomical structure. The frond of Microrhinus is polystro- 

 matic throughout, also the margin of the lamina, save for the very tip. In this it agrees 

 with Pantoneura. The formation of cortex is illustrated in fig. 12 b — c. The cross sec- 

 tion through the marginal parts (fig. 12 d) counts about five cell layers. The formation 

 of hyphae begins early in the costa; in the old midrib the original elements are separated 

 by a thick tissue of hyphal filaments, most of them running longitudinally (fig. 12 e). 

 Hyphae are numerous in the »wings» also, making the midrib less prominent and less 

 defined than in many other members of the family. 



