ASPIDIUM GAMETOPHYTE 313 



III. Wash a fresh, well-developed pro thallus carefully 

 in water, so as to remove the soil from the root-hairs : 

 mount it whole in water, with the lower surface 

 directed upwards, and examine it with a low power. 

 Observe again the chief points seen above with the 

 naked eye, which are now more plainly visible, and note 

 especially 



1. The form and structure of the cells in the 

 lateral, thinner portions of the prothallus; they are 

 polygonal, and have thin cellulose walls, and proto- 

 plasm containing a nucleus and numerous chlorophyll- 

 corpuscles : the cells at the margin are often extended 

 as hair-like outgrowths. 



2. The cells composing the cushion are of similar 

 structure, but are aggregated in a mass more than one 

 layer of cells in thickness : many of the cells will be 

 seen to have grown out as root-hairs. 



3. The depressed apex of the prothallus, which is 

 occupied, not by a single wedge-shaped cell, as is the 

 case in early stages of development, but by a closely 

 aggregated series of marginal cells, with thin cell- 

 walls, and every appearance of recent and repeated 

 cell-divisions. 



4. The antheridia, which are hemispherical out- 

 growths, situated chiefly on the posterior and lateral 

 portions of the underside of the prothallus. 



5. The archegonia, which are situated on the 

 cushion near to the organic apex of the prothallus ; the 

 multicellular neck of the archegonium projects from 

 the surface of the prothallus as an elongated cylindrical 

 structure. 



Under the low power select one mature antheridium, 



