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THE PTERIDOPHYTES 439 
flask-shaped archegonia on the prothallial cushion each of which 
contains anegg. Both kinds of prothallia bear absorptive rhizoids 
on their lower surace. The antherozoids, liberated from the 
antheridia of male prothallia, swim to the archegonia of neigh- 
boring female prothallia, enter their mouths, pass down their 
neck canals and gather about the eggs. In each instance the best 
adapted one fertilizes the egg. The fertilized egg (odspore) 
develops into an embryo which through continued growth becomes 
a mature sporophyte plant. 
THE Cius MossEs 
The Class Lycopodinee or club mosses consists of small peren- 
nial, vascular, dichotomously-branched, trailing, evergreen 
herbs with stems thickly covered with awl-shaped leaves. They 
are represented, today, by over 900 extant species. ‘These are 
relatives of giant tree-like species of club mosses such as Lepido- 
dendron and Sigillaria which with the giant horsetails and ferns 
formed the chief flora during the Coal Age. They differ from 
ferns and horsetails in possessing a suspensor, like seed plants, in 
their early sporophyte stage and in having biciliate sperms. 
Except in a few instances the sporangia are borne on sporophylls 
crowded together and forming cones or spikes (strobili) at the 
ends of erect branches or as lateral branches. The spores found 
within the sporangia are either alike or unlike in size, hence the 
plants are either homosporous or heterosporous. In heterospory the 
small spores give rise to male gametophytes and the large spores 
to female gametophytes. 
Famity I.—Lycopopiace#, including the single genus 
Lycopodium with widely distributed species. The group is 
homosporous. The spores of Lycopodium clavatum are official. 
Lire History or Lycopoprum CLAvAtuM.—This species of 
club-moss thrives in temperate and sub-tropical forests of both 
hemispheres and yields a light-yellow, mobile powder consisting 
of spores. This powder is of value in pharmacy to prevent the 
adhering of suppositories, pills, etc., and in medicine as a protec- 
tive to tender surfaces. When examined under the microscope 
the spores appear tetrahedral with one convex and three plane 
surfaces.. The outer wall (exosporium) of each is reticulated, 
