Po? EQUISETACE. 
Group PTERIDOPHYTA. 
(VASCULAR CRYPTOGAMS.) 
Plants with a highly organized sporophyte generation, possessing 
true vascular (conducting) tissue, and true roots. 
With the exception of Jséetes, Botrychium, Helminthostachys, 
and, according to recent observations, Hguisetum,! there is no 
secondary thickening in the vegetative structures of the living 
genera included in this group. Among fossil genera secondary 
thickening appears to have been common. 
The Pteridophyta differ from the Bryophyta in the greater advance 
in physiological division of labour as expressed in the more com- 
plete differentiation of tissues. The presence of a true vascular 
system and the possession of true roots at once separate the 
Pteridophyta from the next lower group of plants. In the 
higher group the sporophyte generation is the more conspicuous ; 
in the Bryophyta the gametophyte (oophyte) generation is more 
prominent. 
Class EQUISETIN &. 
Leaves in whorls and small in proportion to the stem, in the 
form of sheaths, with long or short teeth, clasping the stem at 
the nodes. : 
The fertile branches terminate in spikes formed of leaves 
modified in the form of peltate scales arranged in close whorls 
with sporangia attached to their inner surface. 
Family EQUISETACE A. 
Contains the single recent genus “guwisetum, and the fossil 
species included under the generic name Lguisetites. 
1 Cormack, Annals Bot. vol. vii. 1893, p. 63. 
