EMBRYOLOGY 



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By this means rapid growth of the root (Fig. 169, B, r.) takes 

 place, and it soon pierces the prothallus and penetrates into the 

 soil. Simultaneously the first leaf (/.), carrying with it the still 

 rudimentary stem (s.), emerges on the lower side, and, arching 

 up through the notch at the front end of the heart-shaped pro- 

 thallus, exposes its green blade to the light. The stem now 

 grows more vigorously, giving rise to adventitious roots which 



9. 



FIG. 168. a-c, archcgonia, e,f, andg, antheridia, and d, single spermatozoid 

 of the Fern, a, immature, and b, mature, archegonium in longitu- 

 dinal section ; c, neck in surface view, o., egg ; v.c., ventral canal 

 cell, g, almost mature antheridium in optical section, showing the 

 wall (w.) and the spermatozoid mother-cells (s.) ; e, dehiscing antheri- 

 dium with the escaping spermatozoids ; /, dehisced antheridium from 

 above, (a after Goebel ; the remainder after Kny.) 



replace the short-lived primary root, and it is not long before 

 further leaves develop (Fig. 169, C). The latter, however, show 

 but a very gradual increase in complexity, from the first, often 

 almost undivided leaf, to the normal compound foliage of the 

 adult Fern, which is frequently only attained after the lapse of 

 several years. Production of sporangia is generally deferred till 

 this stage is reached. 



The young Fern, like the sporophyte of Liverworts and 

 Mosses, is thus for a time dependent for nourishment on the 



