GENERAL INTRODUCTION I/ 



outgrowth from the middle of the anterior cut-edge, as shown in 

 Fig. 9, A, A 2 , that gradually enlarges to form a new thallus. It will 

 be seen from the figures that the whole anterior edge does not grow 

 forward, but a new thallus arises from a group of cells at, or near, 

 the anterior edge. These cells are the least-differentiated cells in 

 the piece, and have softer cell walls than have the other cells. 



FIG. io. After Pringsheim. A. A piece of seta of sporophore of Hypnum cupressiforme, sending 

 out protonema-threads. B. Longitudinal section of a piece of the seta of sporophore of 

 Bryum catspitosum. C. Piece of same of Hypnum cupressiforme. Moss-plant arising from new 

 protonema. D. Piece of same of Hypnum serpens with protonema and moss-plant arising 

 from it. 



Pringsheim has shown that if a piece of the stalk of the sporan- 

 gium of certain mosses is cut off, it produces at its ends thread-like 

 outgrowths which are like the protonema-stage of the moss, and from 

 this protonema new moss-plants may arise (Fig. io, A, B, C, D). 



Braefeld has obtained a somewhat similar result in one of the 

 moulds, in which a piece of the sporangium stalk gives rise to a 

 mycelium from which new sporangia may be produced. 



