128 



THE THEORY OF EVOLUTION 



(spore-bearing) leaves specially changed. The fertile 

 leaves are not confined to definite parts of the caudex 

 and do not limit its growth. 



The ' Water Ferns ' are small plants with a hori- 

 zontally growing stem which creeps on the ground or 

 floats on the water. They are heterosporous i.e. they 



produce in separate vessels 

 micro- and macrospores ; the 

 true Ferns are homosporous, 

 with only one kind of spore. 



Class 2: Equisetinse 

 (Horsetails). 



(a) Herbaceous (all the 

 present forms) ; the leaves 

 relatively small, undivided, 

 arranged in whorls, and 

 branched (Fig. 30). 



(b) The spore capsules are 

 situated on peculiarly meta- 

 morphosed leaves which are 



conjoined into a single bloom (so called) which terminates 

 the growth of the shoot. The branches are arranged 

 in whorls i.e. they spring at even distances and all in 

 the same plane on the stem. 



Class 3 : Lycopodinae (Club -mosses). 



(a) Herbaceous (all the present ones) ; the leaves 

 very small and simply constructed (almost scale-like). 



(b) The sporangia (spore vessels) are situated singly 

 on the base of the upper side of the leaf, or in the leaf 

 axis, or above the axis on the stem itself. 



FIG. 30 . HABIT OF AN EQUISE- 

 TUM (Equisetum arvensc). a, 

 barren shoot ; b, fertile shoot ; 

 c, portion of stem. 



