STRUCTURE AND DEVELOPMENT. 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 Oharss possess a somewhat 

 similar cell at their base but it differs from that of 

 the NltelldR 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 

 Coronula. JL 



ot structure which serve to dirterentiate 



the two principal divisions of the Charophyta. ID 

 the Nltellese 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 Chares the coronula is formed of five cells 

 (Fig. 21), 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. 



The process of fertilization has been 

 Fertilization. i , \ ,- 11^-^-0 



exhaustively investigated by Ue rJary 



in the case of Gkara vulgaris, and described in his 

 6 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, 



