AMONGST THE SEAWEEDS. 35 



dust will be found crowded with the most bewitching 

 forms, and is well worth mounting for future 

 entertainment and study. 



Diatoms are propagated usually by cell-division. 

 By this process one cell becomes two, and these 

 again divide. The cell-contents first divide, and each 

 portion begins at once to grow a new valve. When 

 this is completed the two parts separate, each pos- 

 sessing one of the old valves and a new one, and 

 thus two perfect plants replace one old one. Professor 

 Smith studied these processes some thirty years 

 ago, and came to the conclusion that self-division 

 occupied about twenty-four hours. If this is correct, 

 the progeny of a single diatom would amount to a 

 thousand millions in a month. This process is 

 analogous to gemmation, and is something like the 

 growth of a tree by budding. After awhile, how- 

 ever, the vital energy of the cells seems to be 

 exhausted, and then a true generative process is set 

 up. The cell contents of two parent frustules unite 

 in some mysterious way and produce new genera- 

 tions. 



Of these microscopic Algae the number of species 

 is simply bewildering. It is so recently as 1824 

 that Agardh published the first systematic arrange- 

 ment of them, and he recorded forty-nine species. 

 Now, however, they are numbered by thousands. 

 Their exhaustive study is quite enough to occupy 

 the whole leisure of any one individual, and it is not 

 to be expected, therefore, that I can give here a 

 complete account of them. But let it not be thought 

 that they are contemptible or unworthy of investi- 



