14 



POND LIFE 



divided into two halves by a waist. When reproduction takes 

 place the " waist " becomes narrower and narrower, and even- 

 tually breaks. At the same time another plant undergoes 

 similar changes. A most remarkable phenomenon now takes 

 place. The contents of the half cells of the first Desmid leave 

 their cell walls, and simultaneously the cell walls of the second 

 Desmid are evacuated. The cell contents meet, and very soon 

 are surrounded by a thick wall, covered with peculiar spines. 

 This structure is the spore case, and in it the spores are formed, 



DESMIDS 



1. Hyalotheca dissiliens. 2. Cosmariurn botrytis, multiplying. 

 3. Closterium lunula, dividing. 





and remain dormant until the following spring, depending on 

 when the conjugation took place. 



Another most interesting Desmid is Hyalotheca dissiliens. 

 In this case we find several Desmids living fastened together 

 in a colony surrounded by gelatinous matter. When conjuga- 

 tion takes place the contents of two neighbouring cells fuse, 

 and a spore case is formed. 



Desmids can be easily kept for study. If placed in a watch- 

 glass in water obtained from their natural home, they will not 

 only live, but increase rapidly. Before leaving Desmids, men- 

 tion must be made of their power of movement. Similar to 

 diatoms, they are able to travel freely, and, so far, no means of 



