i'SS INTRODUCTION TO CRYPTOGAMIC BOTANY. 



various warm climates, none of the species occurring so far 

 north as our own coasts. Batrachospermum occurs in the 

 Ganges, in North America, Hermite Island near Cape Horn, 

 and New Zealand ; and Thorea is found in the latter country, 

 and in Bourbon. B. vaguni, of New Zealand, is not distin- 

 guishable from specimens gathered on Snowdon. One curious 

 circumstance in the genus Batrachospevmum, of which, as 

 mentioned above, we shall find instances again, amongst the 

 rose-coloured Algae, is that the threads of the knot-like masses 

 send decurrent joints down the stem, thus making that com- 

 pound which was originally simple. The genus is not con- 

 fined to fresh water ; one species at least flourishes in the sea. 

 They are exactly analogous to Mesoglcea amongst the Melano- 

 sperms, and to Crouania, &c. amongst the Rhodosperms. 



6. HYDRODICTYEiE, Dcn. 



Threads forming a reticulated sac, producing minute zoospores 

 from their endochrome. Zoospores arranging themselves into 

 polygons, and at length uniting and swelling into new nets. 



111. A small but singular tribe of Algae, remarkable 

 alike for the net-hke form and singular mode of repro- 

 duction. The common Hydrodictyon utriculatum is found 

 in ponds, and resembles a long purse with regular reticula- 

 tions. At first sight, the joints of which the net- work is com- 

 posed appear like those of an ordinary Conferva, consisting 

 of two sacs, one within the other, of which the inner contains 

 a granular endochrome; after a time, however, these joints 

 swell, and ultimately, by the organization of the endo- 

 chrome, become so many new plants. Dr. Areschoug* has 

 pointed out, in a very interesting paper, the mode in which 

 this change takes place. The granular mass gives rise, at a 

 certain period of growth, to a number of elliptic grains endowed 

 with active motion. These become attached to each other by 

 their extremities, so as to form a net-work ; union takes place 

 between the several bodies, and in process of time a new indi- 

 vidual is formed, which becomes free by the absorption of the 

 external walls. If the genera Microdictyon and Tcdero- 

 dictyon really belong to this group, the species grow in salt as 

 * Liuu. V. xvi, tab. 5, aud De liydrodictyo utriculari Dissert. 



