THE VASCULAR CRYPTOGAMS 73 



plant to the prothallus and to take up food from it until 

 the embryonic stage is past (see Fig. 37,/). 



Growth and accompanying cell-division go rapidly on ; 

 the parts which develop quickest are the root and first 

 leaf ; for a long time the stem remains very rudimen- 

 tary. The ventral part of the archegonium becomes 

 much enlarged, to make room for the developing embryo. 

 The root is the first part to break through, whereupon 

 it makes its way down into the soil. It is soon followed 

 by the first leaf, which turns upwards between the lobes 

 of the prothallus, and spreads out its blade to the light. 

 Meanwhile the foot is absorbing the food produced by 

 the prothallus, but this is soon exhausted, and then 

 the embryo becomes an independent plant, which con- 

 tinues its growth, producing fresh leaves and roots. 

 The leaves which are first formed are always of a 

 comparatively simple shape, and it is only gradually 

 that the. successive leaves assume the form characteristic 

 of the species. At the same time the stem increases 

 in bulk, and its anatomical structure becomes more 

 complex. 



We have now traced the normal life-cycle through 

 its complete course, and have got back to the asexual 

 generation, or sporophyte, from which we started. 



E. COMPARISON BETWEEN THE LIFE-HISTORY OF FERNS 



AND THAT OF THE HIGHER PLANTS 



In the Ferns, for the first time, the occurrence of a 

 distinct alternation of generations becomes manifest. 

 In these plants the prothallus, though small, is just as 

 distinct an individual, and leads just as independent a 

 life as does the asexual Fern -plant itself. In fact, we 



