STRUCTURE AND DEVELOPMENT. 



51 



and therefore in the opposite direction to the torsion 

 of the stem (Fig. 21 v). The upper cell remains short, 

 and in the Nitellese is again divided into two by a 

 horizontal septum (Fig. 22, dd). The five or ten upper 

 cells, as the case may be, combine to form a crown to 

 the oogonium — the coronula. 



The five elongated cells adhering along their lateral 

 lines of contact form an envelope (Fig. 22 i-iii) which 

 encloses the oosphere. These spiral cells are usually. 



Fig. 21. — Development of oogonium of Chara vulgaris (after De Bary 

 and Migula). a, oosphere; b, node-cell; c, enveloping cell; d, 

 cells of coronula ; e, turning cell. i. First division of cell of future 

 oogonium, ii. I)ivision of periphery of node-cell into five cells 

 forming the enveloping cells of oospore, iii. Further development 

 of the five enveloping cells, iv. Formation of horizontal septum 

 dividing enveloping cells into two stages— the upper forming the 

 coronula. v. Further development of enveloping cells, showing 

 their lengthening and spiral growth and formation of turning cells, 

 vi. Oogonium approaching maturity. 



if not always, either of a greenish or orange colour. 

 As the oosphere increases in size the enveloping cells 

 continue to elongate and the spiral become more 

 pronounced (Fig. 21 vi). 



The oosphere with its enveloping cells, constituting 

 the oogonium, assume a sub-globose, ellipsoidal, or 



