166 
'Polygamia*, 
wards the earth increase in size, and at last strike into 
the ground and become stems. New branches push 
out, which, as they extend, again form roots and new 
stems, till at last a single tree becomes the parent of an 
extensive grove. 
CLASS XXIV. 
CR YPTOGAMIA. 
In this class the parts of fructification are so minute 
that they cannot be arranged according to the princi- 
ples observed in the preceding classes ; but the plants 
which it includes are considerably different in their 
structure and habits from the other vegetable tribes ; it 
is divided into five orders. 
Order I. Filices, or Ferns* 
This order is subdivided into three sections, which 
are characterised by the fructifications being! spiked, 
arranged on the under surface of the leaf or frond, or 
being near the root. 
Equisetum. Gen. diar .-—^ Catkin with peltated 
scales including the parts of fructification ; small in- 
volucrums, two-valved ; seeds numerous, naked, infold- 
ed by four filaments producing pollen. 
Equis. Palustre , Marsh Horsetail 5 with angular 
branched stems ; fructifications on the summit ; branches 
