ULOTHRIX. 71 



are going forward, note in those which are growing in 

 a vegetative manner the following structural points : 



1. The cylindrical unbranched form of the Alga. 



2. The septa, dividing the filament into a number of 

 short cylindrical, or slightly barrel-shaped cells, of more 

 or less unequal length. Note cases where cell-division 

 is in progress, or only recently completed. 



3. The base of attachment, which is usually 

 attenuated, colourless, and often branched so as to 

 obtain a hold on the substratum : granules of soil, &c., 

 will usually be found attached to it. 



4. The smooth cell-walls, consisting of a thin, 

 outer, mucilaginous layer, and an inner, denser layer 

 immediately surrounding the protoplasm. 



5. The protoplasmic body, in which will be 

 found 



a. A single nucleus, in a lateral position, and more 

 easily recognised after staining with an iodine 

 solution. 



6. A median zone-like chlorophyll body, or chro- 

 matophore, which has the form of a flattened but 

 divided ring. 



c. A central vacuole. 



Associated with Ulothrix will often be found the following Algae 

 which are allied to it : viz. Stigeoclonium, of which the filaments 

 are similar to those of Ulothrix, but differ in being profusely 

 branched ; and Chcetophora, which also consists of branched fila- 

 ments, but they are connected by their swollen cell- walls into a 

 more or less spherical gelatinous mass. 



The reproductive processes are best seen in spring or 

 early summer, and are encouraged by a gentle rise of 

 temperature : they may be best observed in material 



