Survey of Plant Kingdom 137 



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The latter forms a multicellular embryo which develops into a new sporo- 

 phyte. Hence, there is alternation of generations. There are approxi- 

 mately 25 species. 



Examples: Horsetail (Equisetum) (Fig, 49). 



,£later 



^^^^ Archeqonmm 



t-Hhi^oid 



Fig. 49. — Common horsetail or scouring rush (Equisetum) of the subphylum. 

 Sphenopsida, class Equisetineae. A, Sterile, vegetative branch (left) and fertile, 

 reproductive branch (right) ; B, one unit of a strobilus much enlarged to show 

 several sporangia; C, prothallus with antheridia for sperm production and an 

 archegonium for egg (ovum) production; D, gametophyte with archegonia for 

 ovum (egg) production and antheridia for sperm production; E, embryo of horse- 

 tail plant developing from a fertilized ^%g in the gametophyte. The embryo con- 

 sists of two primary leaves, a stalklike foot, and a primary root. The prothallus 

 eventually disappears and the embryo develops into a mature plant with both kinds 

 of aerial branches, as shown in A. 



C. Subphylum Pteropslda (ter -op' si da) (Gr. pteris, wing or fern; 

 opsis, appearance ) . — 



Ferns. — The true ferns belong to'^the class Filicineae (fil i -sin' e e) 

 (L. filix, fern). The sporophyte consists of true roots, stem and leaves; 

 the leaves are generally large, or megaphyllous (Gr. me gas, large), and 

 in ferns are commonly called fronds. The vascular system is rather well 

 developed (Figs. 50, 51, 68, and 69) . 



Multicellular sporangia are borne in clusters, called sori (so' ri) (Gr. 

 soros, heap), on the lower surface of the leaves or on the margins in cer- 

 tain species. In the ferns, the sporophyte is large and independent when 

 mature, while the gametophyte is small, free living, and also independent. 

 This is in contrast to the higher plants in which the gametophyte is de- 

 pendent upon the sporophyte. There is an alternation of generations. 



