184 



FOOTNOTES FROM 



yellow or red. They are delicate as hoar-frost, and seem 

 more like the strange vegetation produced on our window- 

 panes on a cold frosty morning, than veritable living plants. 

 These little organisms, we must not forget, exquisitely 

 beautiful and curious in form and structure as we find 

 them under the microscope, appear to the naked eye a 

 mere green or dark-brown film, or indefinite slimy scum, 

 on the leaves of an aquatic moss, or the stalk of a sea- 

 weed ! 



The propagation of the diatomaceae is performed in a 



FIG. 26. ACHNANTHES ujfiPDJTCTATA slightly and much magnified. 



very singular manner. At certain stages of their growth 

 the frustules or fragments of which they are composed, 

 separate in some species into two portions, each of which 

 forms around itself a cell-wall, possessing a form and 

 character precisely similar to those of the original one ; 

 and thus a very material increase in the number of 

 frustules is, through course of time, effected. This pro- 

 cess is called fissiparous or merismatic division. In 

 some cases the process of reproduction is performed by 

 the conjugation of two approximated filaments, as was 

 seen in the case of the larger confervse, the result being 



