FERNWOKTS AND SEED-PLANTS. 



63 



of nutrition has been shifted from the gametophyte to the 

 sporophyte; and this even when the gametophyte has its 

 largest size and greatest duration, while nutritive work is 

 wholly abandoned in the smaller forms. The sporophyte has 

 also become the long-lived stage, the gametophyte being 

 usually transitory (only exceptionally living more than one 

 season), while the sporophyte lives through one season in the 

 few annuals, and commonly for several or even many years. 



72. The embryo. — The fertilized egg, from which the 

 sporophyte arises, develops while still embedded in the 

 gametophyte in which it is formed. Consequently the 

 embryo sporophyte is, as in the mossworts, at first surrounded 

 by the gametophyte (figs. 76, 

 77). The part of the gamet- 

 ophyte adjacent to the embryo 

 grows under the stimulus of its 

 presence, but the growth of the 

 embryo is more rapid, and it 

 consequently spreads apart the 

 gametophyte (see figs. 76, 77). 

 A portion of the embryo de- 

 velops a temporary organ, the 

 foot, which remains embedded 

 in the gametophyte until the 

 first root, stem, and leaf have 

 been formed (fig. 78). Soon 

 thereafter the gametophyte per- 

 ishes and the foot, no longer 

 useful, disappears. 



73. Members. — The mature 

 sporophyte is differentiated into 

 root, stem, and leaves. The 

 important adaptations of the 

 structure and forms of these members are so similar to those 



Fig. 78. — The same as fig. 77, older. 

 The gametophyte, /, seen from be- 

 low, with rhizoids ; the sporophyte 

 still attached but with primary leaf, /, 

 developed into blade and stalk ; /. the 

 primary root: 2, a secondary root, 

 arising from the juncture of leaf-stalk 

 and stem. Magnified about 4 diam. — 

 After Sachs. 



