xxx DEVELOPMENT OF SPOROGONIUM 405 



axial row at first similar to those of the wall. As the ovary 

 develops, the proximal or lowermost cell of the axial row 

 takes on the character of an ovum (B 2 , ov) ; the others, called 

 canal cells (en. c\ are converted into mucilage, which by its 

 expansion forces open the mouth of the flask and thus makes 

 a clear passage from the exterior to the ovum (B S ). 



Through the passage thus formed a sperm makes its way 

 and conjugates with the ovum, producing as usual an 

 oosperm or unicellular embryo. 



The development of the embryo is at first remarkably 

 like what we have found to take place in Hydroids (p. 246). 

 The oosperm, having surrounded itself with a cell-wall, 

 divides into two cells by a wall at right angles to the long 

 axis of the ovary : each of these cells divides again re- 

 peatedly, and there is produced a solid multicellular embryo 

 or polyplast (c 1 , spgnni). 



Very early, however, the moss-poly plast exhibits a striking 

 difference from the animal polyplast or morula : one of its 

 cells that nearest the neck of the ovary takes on the 

 character of an apical cell, and begins to form fresh seg- 

 ments like the apical cell of the stem. Thus the plant 

 embryo differs almost from the first from the animal 

 embryo. In trie animal there is no apical cell : all the 

 cells of the polyplast divide and take their share in the 

 formation of the permanent tissues. In the plant one cell 

 is at a very early period differentiated into an apical cell, and 

 from it all cells thereafter produced are, directly or indirectly, 

 derived. 



The embryo continues to grow, forming a long rod-like 

 body (c 2 , spgnni] the base of which becomes sunk in the 

 tissue of the moss-stem, while its distal end projects vertically 

 upwards, covered by the distended venter (v) of the ovary. 

 Gradually it elongates more and more arid its distal end 



