54 



MOSSES AND FERNS 



CHAP. 



than six in all. In Targionia (Fig. 21, A), and Strasburger^ 

 observed the same in Alarchantia, the ripe egg shows a distinct 

 " receptive spot," that is, the upper part of the unfertilised 

 egg is comparatively free from granular cytoplasm, while the 

 lower part, about two-thirds in Targionia, is much more densely 

 granular. The nucleus is not very large and has very little 

 chromatin. The nucleolus is large and distinct and stains very 

 intensely. As the archegonium of Targionia matures, its 

 neck elongates rapidly and bends forward and upward, no 



Fig. 17. — Targionia hypophylla (L.). A, Longitudinal section of the apex of the thallus, with young 

 archegonia (ar), x 525 ; x, the apical cell ; B, j'oung ; C, older archegonium in longitudinal 

 section ; D, cross-section of the archegonium neck, X 525. 



of the 



the 



archegonium 



archegonium 



IS 



neck is 

 upon the 



doubt an adaptation to facilitate the entrance of the sper- 

 matozoid. A similar curving 

 observed in other forms where 

 lower side of the receptacle. 



After an archegonium (or sometimes several of nearly 

 equal age) is fertilised, the growth in length of the thallus stops, 

 but there is a rapid lateral growth with results in the formation 

 of two valves, which meet in front much like the two parts of 

 a bivalve shell, and this involucre completely encloses the 

 young growing sporogonium. 



^ Strasburger (2), p. 418. 



