214 PRACTICAL BOTANY 



Attention should be paid to the mode of attachment of the fila- 

 ments to the shields : in a mature antheridium which has been 

 burst by very gentle pressure, observe that an elongated cell, the 

 mamibrium, rises from the centre of the inner surface : this is 

 terminated by a head-cell, which supports six secondary heads, 

 and to each of the latter are attached four of the antheridial 

 filaments : their total number is therefore about 200. 



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. 



VIII. Examine mature oogonia and note the dark colour, and 

 the thickened, lignified wall of the spiral cells, while the 

 oospore itself is surrounded by a thick, colourless wall. Burst 

 one by pressure upon the cover-slip, and it will be seen that 

 the contents consist largely of starch and oil. 



IX. The results of germination may be readily observed in 

 Chara or Nitella, if specimens with mature oospores be kept in 

 water in a bell-glass through the winter : in the spring the 

 oogonia which had settled to the bottom may be found in various 

 stages of germination. Some may be seen still closed at the 

 apex : in others the spiral cells may have ruptured at the apex 

 and two or more transparent filaments project : one of these 

 develops more strongly as the proembryo, it divides by trans- 

 verse walls, and assumes a green colour : the other remains 

 colourless and develops into rhizoids. In one of the filaments 

 which is far advanced observe a narrow, disc-shaped cell, two 

 or three cells short of the apex- this is the stem-node : from it 



