THE ALG^E 169 



71 and 72) according to the species, but the number is 

 not always constant even in the cells of the same 

 filament. Each chloroplast is studded at intervals with 

 large pyrenoids, which can be well seen here, and have a 

 crystalloid form. It is around these proteid bodies that 

 the starch is formed when assimilation is taking place. 

 Each pyrenoid then becomes surrounded by a coating of 

 minute starch-granules. In every cell there is one 

 large nucleus, either imbedded in the primordial utricle, 

 or suspended in the middle of the cell by protoplasmic 

 fibrils. These fibrils are attached, at the ends remote 

 from the nucleus, to the chloroplast, abutting on it at 

 the points where the pyrenoids are situated. The 

 nucleus contains a large nucleolus. 



All the cells are similar, and all take an equal part by 

 growth and transverse division in the development of 

 the plant. Spirogyra may therefore be spoken of as 

 physiologically a unicellular organism, for all its cells are 

 equivalent, and each appears to be capable of carrying on 

 all the necessary functions for itself. In the ordinary 

 state the plant is morphologically multicellular, but some- 

 times the thread actually breaks up into its separate cells, 

 and we then find that each of these on its own account is 

 capable of independent life, and can start a new plant. In 

 a large number of species allied to our type, the cells 

 normally lead an isolated existence, separating after each 

 division. This is usually the case in the Desmids, a Family 

 of freshwater microscopic plants of great beauty. 



In Spirogyra the division of the cell coincides with 

 that of the nucleus, which takes place by a complicated 

 process (much like that in the higher plants) resulting 

 in the formation of two exactly similar daughter-nuclei. 

 While this is going on, a transverse septum gradually 



