134 Pla?it Biolooy 



change of gases, and a protectixe layer of waxlike cutin, in certain parts. 

 The sporophyte is larger than the rather inconspicuous gametophyte, 

 and the former is independent when mature. Hence, there is an alter- 

 nation of generations. Tracheophytes are primarily terrestrial, although 

 some live in water. The development of plants with vascular systems is 

 one of the great steps in the evolution of plants. A recent theory suggests 

 that the vascular plants may have evolved from some algal ancestor, 

 probably from the Chlorophyta. All possess multicellular sex organs, and 

 multicellular embryos are developed from the fertilized egg (zygote). 



A 



C 



Fig. 46. — Bog or peat moss (Sphagnum) of the phylum Bryophyta, class Musci. 

 A, plant showing terminal antheridial (male) branches (at tip) ; B, antheridium 

 (in section) producing sperm; C, archegonium (in section) showing egg and 

 elongated neck; D, plant showing terminal sporophytes (at tip) ; E, sporophyte 

 (in section) showing basal foot for attachment to gametophyte, the seta, and the 

 production of spores; F, leaflike organ (surface view) showing cells containing 

 chloroplasts and other clear, dead cells for water storage: the latter connect with 

 the outside by means of pores; G, protonema (young thalloid gametophyte) from 

 which the erect, adult gametophyte will arise; rootlike rhizoids are shown. 



A. Subphylum Lycopsida (laik -op' si da) (Gr. lykos, wolf; opsis, 

 appearance). — The club "mosses" belong to the class Lycopodineae 

 (lai ko po -din' e e) (Gr. lykos, wolf; pous, foot). The sporophyte con- 



