STRUCTURE AND DEVELOPMENT. 



47 



III 



IV 



JTiQ. 18. — Development of antheridium of Nitella fiexilis (after Sachs), 

 i. Early stage showing young antheridium divided into eight equal 

 parts by the growth of two vertical walls, at right angles to one 

 another, and a horizontal wall. ii. Further stage showing each 

 eighth part divided into an exterior and interior portion, iii. Later 

 stage showing interior portion again divided, making three layers, 

 the outermost expanding tangentially to form the plates or shields, 

 the middle growing radially to form the mauubria, and the inner- 

 most forming the head-cells which bear the filaments, iv. Section 

 of antheridium at still later stage showing further development 

 of parts, a, cell which in ii-iv divides into (b) flask-cell and (c) 

 extra basal cell ; d, branchlet node ; e, branchlet internode ; /, 

 lateral ray ; g, young oogonium. In i-iii the protoplasm has been 

 contracted by glycerine. 



