416 PRACTICAL BOTANY 



weak acetic acid and glycerine. In such preparations it may be 

 ascertained that the antheridium arises in place of an adaxial 

 leaflet ; from the single cell a pedicel is first cut off, and the head 

 then divides into octants : each octant undergoes periclinal divi- 

 sion, the inner cell again dividing. The outermost cells form the 

 shields, the middle series the manubria, while the innermost series 

 of eight give rise by growth, budding and repeated divisions, to the 

 capitula, secondary capitula, and antheridial filaments. By careful 

 staining of the latter in various stages of their growth illustrations 

 of the development of the spermatozoids may be obtained. 



The antheridia of Nitella are similar in structure to those of 

 Chara, but differ in their position, being developed from the 

 terminal cell of the leaf ; accordingly it is easier to trace the 

 development in Nitella, 



VII. Mount in water a leaf bearing one or more 

 mature but unfertilized oogonia or " nucules " as they 

 are sometimes called, and examine under a low power. 

 Observe their position, directly above an antheridium : 

 their oval form, and insertion by a short pedicel. Each 

 consists of an outer coat, composed of five spirally 

 twisted cells, a crown or apical rosette of five cells, and 

 a large central ovum : at the base of the latter when 

 young, or after treatment with potash, a short cell is to 

 be seen. Note that a narrow lateral slit may be seen 

 between the cells of the crown at the receptive period, 

 through which the spermatozoids may pass to the 

 ovum. Attempts may be made to see the entry of 

 the spermatozoids by adding a drop of water containing 

 motile spermatozoids to a preparation in water of a 

 mature oogonium. 



Sections should be cut longitudinally through the 

 oogonium : this may be done by hardening in alcohol, 

 and embedding in paraffin : in sections thus prepared 

 the details of internal structure, which are only seen 



