INTRODUCTION TO CRYPTOGAMIC BOTANY. 139 



well as fresh water, and are widely distributed, as in the Red 

 Sea, Sandwich Islands, Atlantic Ocean, and Nagasaki. The 

 affinity of these two genera is possibly rather with AnadyoTnene, 

 to which genus one at least is referred by Dr. Montagne. If 

 these are excluded there is but a single representative, which is 

 too pecuUar in its characters to admit of union with any other 

 group. This curious production inhabited the pond in the Old 

 Botanic Garden at Cambridge, for many years. I believe Pro- 

 fessor Henslow was the first to point out the origin of new plants 

 from the individual joints, specimens illustrative of which I re- 

 ceived from him more than thirty years ago. In this state it 

 is scarcely possible to conceive a more attractive object for the 

 microscope. 



7. NoSTOCHINBiE, Ag. 



Threads very slender, moniliform, invested with gelatine, 

 which is at length to all appearance common to the mass, but 

 at first apportioned to each individual thread ; propagation by 

 the division of the threads, or by zoospores. 



112. Though the species of which this section is composed 

 agree closely in character, their habit is very different. The 

 thin stratum of some species of Anabavna, differing Httle in 

 appearance from some minute Conferva, when compared with 

 one of the almost gigantic species of Nostoc, which float in 

 the lakes of Thibet, or occupy damp ground in New Zealand, 

 seems at first sight to be widely different, and yet there is a 

 close series of forms leading up directly from the most humble 

 to the most highly-developed species. All are characterised by 

 necklaces of spores, surrounded for the most part by firm and 

 copious jelly, of which some privileged joints are larger than 

 the rest. The gelatinous element sometimes forms large wavy 

 expansions or pruniform bodies, but in many it constitutes a 

 mere stratum, sometimes of little density, either floating on the 

 surface of the water, or adhering to the damp naked soil. 

 Thuret was, I believe, the first who directed attention to the 

 mode of increase of these AlgK. He perceived in Nostoc verru- 

 cosum that the threads broke up into fragments, burst through 

 the common envelope, and became dispersed in the water. In 

 this condition they were endowed with spontaneous motion, a 



