30 INTRODUCTION. 



of the Closterina should prove to be of a horny nature, as 

 would appear to be the case from their becoming wrinkled 

 when heated, they would be removed from the vegetable 

 kingdom with still greater certainty." 



Although at first sight it seems to indicate the contrary, 

 the swarming of the zoospores or granules really affords a 

 strong confirmation of the vegetable nature of the Desmidiese. 

 This swarming has been noticed in the Algse by many emi- 

 nent observers, and notwithstanding the extraordinary phae- 

 nomena which it presents, no fact in their history is more 

 firmly established. Hence J. G. Agardh, who so worthily 

 emulates his father's fame, has been induced to apply 

 the name of " Zoospermese" to one of his three primary 

 divisions of the Algse. In this country the swarming has 

 been witnessed by Mr. Borrer, the Rev. M. J. Berkeley, Mr. 

 Hassall, and others. I have frequently seen it in Sphcsroplea 

 crispa and Draparnaldia tenuis. A commotion arises within 

 the cell as if all its contents were suddenly endued with life ; 

 the disturbance increasing, the cell opens, when the zoospores 

 hasten from their prison, and, apparently enjoying their 

 newly-acquired liberty, dart about in every direction, until, 

 tired of their sport, they at length resume a quiescent state*. 



This description has such a marvellous character that the 

 reader may suppose it is somewhat indebted to the imagi- 

 nation, and I believe no one can witness the occurrence for 

 the first time without being startled and almost led to doubt 

 the evidence of sight. Such movements are so contrary to 

 our ordinary experience of vegetable life, that we involun- 

 tarily hesitate to admit their compatibility with it ; and on 

 the continent many eminent naturalists, unable to find a 

 satisfactory explanation, consider that in this stage the zoo- 

 spores are really animals, and do not acquire their vegetable 

 nature until a subsequent period. This opinion never ob- 

 tained countenance in this country : yet a Berkeley did not 



* The fullest details accessible to the English reader will be found in Mr. 

 Harvey's excellent introduction to his ' Manual of British Alga?,' and in the 

 introduction to Hassall's ' British Freshwater Algae,' 



