64 THE SMALLEST LIVING THINGS 



ample, may grow luxuriantly in certain pure lakes and reservoirs, 

 particularly in spring after the reservoirs have been frozen dur- 

 ing the winter. At such times the water has a not unpleasant 

 geranium-like odor which is unquestionably due to Asterionella 

 and probably to their contained oil drops.* 



The method of reproduction of diatoms recalls that of the 

 budding division of the desmids. Multiplication takes place usu- 

 ally at night and is preceded by a slight increase in the volume of 

 the cell. The color-bearing chromatophores and the nucleus 

 divide, their division being followed by that of the protoplasmic 

 mass in a plane parallel with the valve faces. New, very delicate, 

 siliceous valves are secreted about the daughter cells and within 

 the older valves, but with the development of the connecting 

 bands the old valves are forced apart. Being contained within 

 the older frustule it would appear that the daughter diatoms 

 must be smaller than the parent cell from which they came. In 

 some cases this appears to be the case. In other cases, however, 

 the daughter valves are only slightly silicified and may undergo 

 an increase in size before strong silicification sets in. 



A process resembling that of zygote formation in desmids 

 is also common among diatoms. This "auxospore" formation 

 varies widely in different types. In some {e.g., Navicula amphis- 

 bena), the protoplasm of one of the smaller cells, while still em- 

 bedded in jelly, swells up, escapes from its frustule as an auxo- 

 spore and then grows to the full size of the species. In others, 

 the protoplasm divides into two cells, each of which forms an 

 auxospore, e.g., Synedra affinis, or the two cells thus formed re- 

 unite to produce one auxospore, e.g., Achnanthes subsessilis, and 

 in still others the protoplasms of two associated individuals leave 

 their frustules, fuse, and form a single auxospore, e.g., Surirella. 

 In several species each of the two associated frustules divides into 

 two cells, these fuse with the two from the other individual, and 

 two auxospores result. There are wide variations between par- 

 thenogenesis and fertilization processes in this group. 



Still another method of multiplication occurs in some forms. 

 This consists in the multiple division of the cell whereby a num- 

 ber of spores are formed. In certain marine types these spores 



* Consult G. N. Calkins, A Study of Odors Observed in the Drinking Waters 

 of Massachusetts, Reports, Massachusetts State Board of Health, 1892. 



