314 PRACTICAL BOTANY 



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 



a. A wall, composed of a single layer of narrow cells ; 

 this completely surrounds 



b. The spermatocytes, or mother-cells of the sper- 

 matozoids, which are small, and not very numerous. 



Other antheridia may be found which have already 

 burst the outer wall : in these the contents of the 

 mother-cells may perhaps be seen escaping from the 

 ruptured antheridium as spiral spermatozoids, endowed 

 with active movements. 



If a preparation showing motile spermatozoids be treated with 

 a weak solution of iodine, the movements will cease with the 

 death of the spermatozoids, which will assume a brown staining, 

 while the cilia attached to the anterior ends of them will then 

 be clearly seen. 



Select under the low power one mature archego- 

 nium, and then observe it in detail under the higher 

 power. If the neck be vertical, which would under 

 the circumstances be the natural position, since the 

 prothallus was mounted with the lower surface upper- 

 most, there will then be seen, on focussing down upon 

 it, four rows of cells composing the wall of the neck, 

 and surrounding one cell, the canal-cell. 



IV. Treat some prothalli with a saturated solution of 

 picric acid in water for some hours : wash them with 

 water, and then harden them gradually by successive 

 treatment with alcohol of 50 per cent., 70 per cent., 

 and finally with absolute alcohol or strong methylated 

 spirit ; or the material may be hardened at once in 



