398 A TEXTBOOK OF GENERAL BOTANY 
A relationship between the liverworts and ferns is indicated 
by the facts that in both the groups there is an alternation of a 
gametophyte and a sporophyte generation and that the gameto- 
phytes are very similar in both cases. 
CLASS EQUISETINEAE (HORSETAILS) 
This is asmall class of plants containing the single genus 
Eqpusetum. Equisetum, like all other pteridophytes, shows an 

Fie. 446. Cross section of a stem of Lycopodium cernuum, showing radial 
protostele in which phloém occurs between the strands of xylem 
Note the sclerenchyma cells near the outer part of the cortex. (x 45) 
alternation of a sporophytic and a gametophytic generation. The 
gametophyte is a simple thallus bearing archegonia or antheridia. 
The sporophyte consists of an underground rhizome (Fig. 440) 
which produces hollow, erect, aérial stalks. The leaves are 
