14 INTRODUCTION. 



fronds of Desmidiese is by Professor Bailey, who detected 

 various species of Closterium and Euastrum in calcareous 

 marls, collected in New Hampshire and New York by Pro- 

 fessors Hubbard and Hall, and also in marl at Scotchtown, 

 New York, by Mr. Connors*. Professor Bailey informs me, 

 that the specimens from the last-named station, and in which 

 he found several Closteria, Euastra, &c., were taken from 

 below the bones of the Mastodon giganteus. As sporangia 

 of the Desmidiese and other membranous bodies in a fossil 

 state have lately been detected by Mr. Deane and Dr. G. 

 Mantell in the grey chalk of Folkestone, it is probable that a 

 careful search in that neighbourhood would also bring to 

 light the fossil fronds of the Desmidiese. 



The production of the Desmidiese in newly-formed col- 

 lections of water is involved in obscurity. The late Mr. 

 Miller of Penzance pointed out to me an instance of this 

 kind well-worthy of notice. He found Hyalotheca dissiliens 

 and other species of this family in an old water-butt, which 

 stood in a yard remote from any apparent station for the 

 Desmidiese, and derived its water from the clouds alone ; and 

 the question naturally arises, How came the Algse there ? 

 The theory of spontaneous generation has never obtained 

 currency in this kingdom, and for my own part I am not 

 unwilling to acknowledge that there are mysteries in nature 

 which we cannot penetrate. I can therefore only attempt to 

 account for the appearance of the Desmidiese under such 

 circumstances in two w^ays, — by supposing either that the 

 atmosphere contains countless myriads of the sporules of the 

 Desmidiese and other Cryptogamia, w^hich vegetate only 

 when they meet a congenial situation, or that the seeds are 

 conveyed by means of aquatic insects, many of which, it is 

 well known, roam during the night by means of their wings 

 from one piece of water to another. The latter I consider 

 the more probable conjecture. 



The entire question of the vegetation of the conjugating 



* American Journal of Science and Arts, vol. xlviii. p. 340. 



