XVI COMPENDIUM. 



Key to the families and genera. 



a. Floating aquatics. (XH. SALVINIACEAE). 



• Leaves very minute, crowded, with simple venation. 



No. 98. Azolla. 

 •• Leaves small, though well-developed, in opposite rows, with 

 anastomosing venation. No. 97. Salviula. 



a.a. Epiphytics or terrestrials, or no floating aquatics. 



b. Rhizome or main stem creeping in the mud ; leaves long-stalked, 



remote or in distant groups, with the fruit borne on, or at the base 



of, the petiole. (XL MARSILEACEAE). No. 96. Marsilea. 



b.b. Rhizome or main stem not creeping in the mud, or, if so, the 



leaves not long-stalked. 



c. Barren leaves laterally connected so as to form remote, 

 tubular or funnel-shaped sheaths encircling the stem; fertile 

 leaves (sporophylla) free, peltate, forming terminal spikes 

 and bearing the sporangia on the under side, along the 

 margin. (XIII. EQUISETACEAE). No. 99. Equisetum. 

 C.C. Barren leaves not laterally connected; fertile leaves (sporo- 

 phylla) whether or not spicate, bearing the sporangia on the 

 upper side, at the base. 



d. Both barren leaves and sporophylla placed in alternate 

 cycles borne on a tuberous stem; sporangia imbedded. 

 (XVII. ISOETACEAE; not in Malaya). 

 d.d. Sporophylla spicate, if alternate with the barren leaves, 

 then not borne on a tuberous stem; sporangia superficial. 

 e. Sporangia 1-locular. 



f At least the younger leaves provided with a 

 very minute decoloured ligula on the upper 

 side, at the base. (XVI. SELAGINELLACEAE). 

 No. 103. !ielaginella. 

 +f Leaves without a ligula at the base. (XV. LY- 

 COPODIACEAE). No. 102. L<ycopodiuin. 

 e.e. Sporangia 2— 3-locular. (XIV. PSILOTACEAE). 

 f. Leaves small, though well-developed; sporo- 

 phylla 2-foliolate, petiolate; sporangia 2-locular. 

 No. 100. Tanesipteris. 

 f.f. Leaves rudimentary, tooth-like; sporophylla 

 2-dentate, sessile; sporangia 3-locular. 



No. 101. Psilotuni. 



