164 Mr. G. J. AUraan on a new yenus 0/ AlgfB. 



in the animal nature of the beings which constituted his ge- 

 nus Anabaina, that he hesitated not to remove them from the 

 vegetable kingdom. The peculiar motion of reptation which 

 he describes them as possessing, and which he compares to 

 the crawling of worms, would appear to be the chief grounds 

 on which he assumes their animality, and he also tells us that 

 the analysis of Vauquelin and Chaptal is entirely in favour of 

 the animal nature of the Anabaina. 



In the Alga which constitutes the subject of the present 

 paper no such motion could be detected, and the same ap- 

 pears to have been the case with the spiral Alga of Mr. Thomp- 

 son. In all the observations which I have had an opportu- 

 nity of making upon the green matter of the Canal Docks, the 

 vegetable nature of this substance would appear to be fully 

 borne out. The probability of its green colour depending on 

 the influence of light has been already mentioned, and this 

 fact, though not decisive, would yet go far to abolish any claim 

 to animality. The phenomena attendant on the spontaneous 

 decomposition of the Alga are altogether coincident with the 

 same view. When a large mass is placed in a limited quan- 

 tity of water, decomposition soon sets in, the green colour be- 

 comes duller, and finally assumes a dirty ferruginous hue, 

 w hile the microscope can now no longer detect any trace of 

 the original monililbrm structure. A disagreeable odour is at 

 the same time exhaled ; but this odour is altogether different 

 from that of decomposing animal matter, and possesses a purely 

 vegetable character. 



In the paper already alluded to, Mr. Thompson makes a 

 similar remark with respect to the Alga of Ballydrain lake, the 

 odour of which, in a state of decomposition, he compares to 

 that of water in which flax had been steeped (see ' Annals,' 

 vol. V. p. 78). 



So far observations are in favour of the vegetability of the 

 Trichorrni ; at the same time however it must not be forgotten 

 that these curious organisms would appear to possess the power 

 of changing under circumstances their specific gravity, being 

 sometimes observed collected in large quantities upon the sur- 

 face, sometimes suspended for a considerable depth through 

 the fluid, and sometimes the whole mass will be found to have 

 sunk to the bottom and disappeared, again to rise to the sur- 

 face when circumstances favourable to its appearance should 

 occur. 



All these phaenomena, however, w^onderful and unaccount- 

 able as they are, would hardly justify us in attributing them to 

 spontaneity; they are in all probability dependent on ex- 

 ternal causes, possibly of a meteorological character, and are 



I 



