272 FIRST FORMS OF VEGETATION. 
ideas of vegetable forms which we are accustomed 
to entertain Diatoms are generally colourless ; 
but some species are of a deep green, or rich 
brown, or a pale 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, ex- 
quisitely beautiful and curious in form and struc- 
ture as we find them under the microscope, ap- 
Fic. Prey evenness UNIPUNCTATA—both figures magnified. 
pear 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 diatomacez is performed 
in a very simple manner. At certain stages of 
1 The deposits from Franzenbad, San Fiore in Tuscany, Bilin, 
Bermuda, and Lough Morne in Ireland, are well known as containing 
many of the most beautiful species, and specimens of them are sold 
by dealers in microscopic objects and apparatus. Most of the 
curious forms that are unknown in this country may be obtained 
from Peruvian guano. 
