STRUCT DEE AND DEVET.OPMENT. 53 



apex whence it makes its way downwards (as Goetz 



shows in a series of illustrations), and finally divides 



into three cells at the base of the oosphere. 



The oogonia of the Ghara?. possess a somewhat 



similar cell at their base but it differs from that of 



the Nitellse in that it originates at the base and not 



at the apex, appears at a later stage in the growth of 



the oosphere, and remains single and undivided. 



This organ presents two distinct types 



of structure which serve to differentiate 



the two principal divisions of the Charophyta. In 



the Nitellese- it is formed of ten cells in two tiers of 



five one above the other (Fig. 22, dd), the whole being 



small, colourless, and inconspicuous, in some species 



persistent, in others deciduous. The five cells of the 



lower tier are very small and closely adherent, those 



of the upper tier are often larger and less adherent. 



In the Gliarese the coronula is formed of five cells 



(Fig. 2]), and except in Nitellopsis and Lychnothamnus, 



is larger, much more conspicuous and persistent, 



exhibiting in different species a considerable diversity 



in height and the direction of the cells, which may be 



convergent, erect, or divergent. 



■r, i..i- J.- ^ The process of fertilization has been 

 Fertilizatidn. , ^ . . . . n i t^ -r. 



exhaustively investigated by De Bary 



in the case of Chara vulgaris, and described in his 



' Ueber den Befruchtungsvorgang bei den Charen ' 



(Berlin, 1871), to which admirable piece of work 



those wishing to pursue the matter in greater detail 



should refer. It will suffice for our present purpose 



to state the general facts. *■ 



The oogonium approaches its full development 



before fertilization. At the apex, and therefore at 



their point of contact with the base of the coronula, 



