DIATOMACE.E. 



205 



in the circle of its narrow sphere as perfectly as the 

 more bulky creations above it. The great work of 

 Ehrenberg has made the forms of many of these curious 

 creatures sufficiently known ; and a most elaborate 

 monograph of a portion of them,* recently published in 

 this country, has added much to the general history 

 of the subject, while it affords to British students 

 exquisitely accurate figures and careful descriptions 

 of all the British species of the group illustrated. 

 The plants included in 

 this microscopic world are 

 classed by botanists under 

 two families, the Desmidiece, 

 which exclusively inhabit 

 fresh water, and the Diato- 

 macece, a great number 

 of which are marine. The 

 forms of these minute organ- 

 isms are strange ; they ex- 

 hibit mathematical figures, 

 circles, triangles, and paral- 

 lelograms, such as we find 

 in no other plants, and their 

 surface is often most elaborately sculptured. Isthmia 

 obliquata here figured, is found in spring and early 

 summer on the stems of many of the filiform Algae, 

 where it forms little glittering tufts a line or two in 

 height. It has been brought from many distant parts 

 of the world, both of the Atlantic and Pacific Oceans. 



* Ralfs on British Desmidiese. 

 coloured plates. 



London, 1848. Thirty-five 



