428 PRACTICAL BOTANY 



2. The mode of origin of the branches may be seen to be 

 by bulging out of the eel I- wall laterally below a septum, 

 the outgrowth being subsequently cut off by a trans- 

 verse septum at its base. 

 Under a high power observe the following : 



1. The thick stratified cell- wall. 



2. The protoplasmic body with a large central vacuole. 



3. The chromatophores, of which the polygonal outline is 



difficult to distinguish : pyrenoids are present. 



4. There are a number of nuclei in each cell, and they lie 



internally to the chromatophores, and project into the 

 vacuole : they may best be seen in specimens bleached 

 in alcohol and stained with methyl green or 

 hsematoxylin. 



In summer many of the cells towards the ends of the filaments 

 will be found empty, and with a round hole (ostiole) in the wall : 

 these are empty zoosporangia. In others the protoplasmic body 

 will often appear more dark and granular : such cells will show 

 on examination various stages of production of the zoospores, 

 which when mature escape through the ostiole formed by swelling 

 and subsequent rupture of the cell-wall. 



Zoospores of two sizes have been observed ; larger ventral 

 zoospores which serve for vegetative propagation, and smaller 

 gametes which conjugate. Observations should be made of these 

 and their movements : the details of their structure may be made 

 out by treatment with iodine. 



