COMPENDIUM. XIII 



GENUS 98. AZOLLA. Leaves in 2 opposite rows, 

 deeply 2-lobed, -the fertile ones bearing the 

 sporocarps on the lowest lobe. 



ORDER SPHENOPHYLLALES. 



Contains a single extinct family only. (') 



ORDER EQUISETALES. 



Differs from the Filicales in having the stems always elongate, more 

 strongly developed than the leaves, articulate, mostly hollow, longitudinally 

 ribbed or striated at least when barren, simple or branched, if branched, 

 the branches often in whorls, originating from the bases of the intemo- 

 dations of the stem, with the leaves erected in the bud. 



Leaves placed in whorls, the fertile ones (sporophylla) forming rather 

 compact terminal spikes and bearing several to many sporangia round 

 the under side of the margin. 



SUBORDER I. EQUISETIME.tE (Isospore Equisetales, 



Horse tails). Barren leaves connected so as to form distinctly 

 toothed, tubular or funnel-shaped sheaths enclosing the bases 

 of the internodations of the stem and branches. Sporophylla 

 not connected, scale-like, peltate, stalked. Spores isomorphous, 

 producing prothallia on which mostly are developed either 

 antheridia or archegonia. 



FAMILY XIII. EQUISETACEAE. Characters those of the suborder. 



GENUS 99. EQUISETUM. Characters those of the 

 family. 



(') Sphenophyllaceae. — Poton., in Engl. & Prantl, Nat. Pfl.Fam., I*, 515. 



