TAXONOMY 
239 
which at its various nodes bears rootlets below and fronds above. 
These fronds are highly developed, each being provided with a 
petiole-like portion called a stipe which is extended into a lamina 
usually showing a forked venation. Some ferns possess laminae 
Fig. 1 14 . — Equisetum arvense. P, sterile branch; P l , fertile branch with 
.strobilus, or cone; R, rhizome (underground); T, cross-section of cone, showing 
insertion of sporophylls in a whorl; N, N 1 , sporophylls with pendant sporangia; 
5, S l , S' 2 , spores with coiled elaters (el). (Gager.) 
which are lobed, each lobe being called a pinna. If a pinna be 
further divided, its divisions are called pinnules. The unfolding of a 
frond is circinate and it increases in length by apical growth. On 
the under surface of the laminae, pinnae, or pinnules may be seen 
