THE VASCULAR CRYPTOGAMS 



63 



initial cells, which all take a like share in the subsequent 

 development. The prothallus, which for a short time 

 grows vertically, soon assumes a horizontal position, and 

 henceforth there is a marked difference between the 

 lower side, which is in contact with the soil, and the 





FIG. 31. Full-grown prothallus seen from below, showing 

 archegonia towards the apex, antheridia and root-hairs 

 towards the base. Magnified about 25 diameters. (After 

 Luerssen. ) 



free upper surface. It is from the under-side that the 

 new root-hairs arise, and to this side also the sexual 

 organs are limited. 



A normal full-grown prothallus seen from below is 

 shown in Fig. 31. The middle part, lying just behind 



