INTRODUCTION. 



The majority of the Algie comprised in the subsequent pages of this memoir were 

 obtained by Dr. Wallich in the year 1855 (from July to November inclusive) from the 

 great coal-fiekl of Bengal, in the district of Raneegunge, about 120 miles N.W. of Cal- 

 cutta. The district was at that time the scene of the Sonthal insurrection, which troo])s 

 were sent to quell; and Dr. Wallich, then Field-surgeon of the expeditionary forces, 

 during the intervals of military duty, found time to collect and observe a large number 

 of the local Chlorophyllophycece. It is to be regretted that my friend did not complete 

 his description in the 'Annals', his graphic power being far greater than mine; but science 

 certainly had considerable and highly important additions from him both in his horne 

 voyage and in lus observations, as government naturalist and scientist to the North At- 

 lantic Surveying vessel (H. M. S. 'Bulldog', under the command of Sir Leopold Mac 

 Clintock, R.N.), which were afterwards published in the North Atlantic Sea-bed', and in 

 över 40 other memoirs and papers! 



I have been requested by many correspondents to quote freely from Dr. Wallich's 

 own words, and this I have done wherever practicable, especially in Streptonema and 

 Onychonema, two new genera of the 1860 memoir. The following graphic pictures are 

 too good to be omitted: 



(a) »As might be supposed from the cosmopolite nature of the Desmidiacese generally, 

 a large proportion of the species referred to are identical with those already known to 

 occur in Europé and America. Many hoAvever are new, and these certainly equal, if they 

 do not surpass, any of the hitherto recorded forms in beauty and symmetry. Amongst 

 the more common species a remarkable amount of divergence from the typical character 

 is everywhere to be met with — a circumstance depending, no doubt, on those peculiaritics 

 of soil and climate which, in Lower Bengal, are so favourable to the exuberant and rapid 

 development of the entire vegetable kingdom. Such peculiaritics operate, however, on the 

 more minute tribes in a special degree; for whilst the higher orders of plants are subject 

 only to the regularly recurring changes of a tropical region, and undergo no abrupt or 

 violent transitions as regards habitat, the humbler Algae are borne abroad, during their 

 sporangial state, to great distances, and into positions differing widely in nature from 

 those wherein they were originally engendered. The liability to variation arising Irom 

 this cause must necessarily be extreme; and, therefore, few situations could be found in 



