52 



PEINOIPLES OF PLANT-TERATOLOGY. 



rhizoicls " in their- upper part, and that in Buxbaumia 

 the marginal cells of the leaves elongated into similar 

 rhizoids. Both cases are normal. 



"We will now turn to the formation of adventitious 

 protonemata in the sporophyte generation. 



Stahl experimented with the moss Ceratodon pur- 

 pureas ; he placed sporogonia, whose capsules were 



Fig. 12. — Tortula muralis. Protonemse (p) growing directly from 

 rhizoid (r). (After Westerdijk.) 



nearly mature, but with still unripe spores, under a 

 bell-glass in diffuse light on moist earth. He found 

 that protonemata grew from the chlorophyll-cells at 

 the cut ends of the seta. In the case of capsules the 

 chlorophyll-cells of the third and fourth layer from 

 the surface grew out into protonemal threads. 



The classical researches of Pringsheim also are 

 interesting. He induced protonema-formation from 

 chopped-up pieces of the setaa of mosses. He found 



