206 PRACTICAL BOTANY. 



mount it whole, in water, with the lower surface directed 

 upwards, and examine it with a low power. Observe 

 again the chief points above noted with the naked eye 

 which are now more plainly seen, 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 

 grains : 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 [see above, small 

 type, p. 205], 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 under side 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, 

 and, without moving the slide, adjust the higher power 

 so as to observe the structure of the same antheridium 

 in detail. It will then be seen that it consists of 



