INTRODUCTION TO CRYPTOGAMIC BOTANY. 145 



not, liowever, confined to the genus Trlchodesmium ; some 

 of the common species of Oscillatoria emit a strong odour 

 of sulphuretted hydrogen, similar to that of the common Chara, 

 insomuch that on one occasion I was obliged to have a water 

 tub scraped, to remove the Algae which had taken possession 

 of its sides to such an extent as to be extremely disagreeable, 

 and to cause sometimes severe headache. 



117. The true Oscillatorice, forming a slimy stratum, which 

 though thin at first gradually acquires a certain degree of thick- 

 ness, so as to peel off in flakes, in consequence of the decay 

 of the older growths. They have long been celebrated for 

 the oscillating motion of the threads. It is possible that this 

 motion may, in part, be due to the propagation of the threads 

 by division and ultimate separation of the inclosing mem- 

 brane, to which also their radiation from a common centre, 

 when a small portion is placed on a piece of moistened paper, 

 may be attributable. But, besides this, many species possess, 

 at the extremity, a tuft of delicate cilia similar to those 

 which occur in AnabaiTia,, and which, like those on the spores 

 of (EdogonivAn, are capable of communicating motion to the 

 body on which they are developed. However this may be, it 

 is quite certain that these organisms do not belong to the 

 animal kingdom, the whole history of their development, and 

 their evident connection with undoubted vegetables, making 

 such a notion altogether untenable. A few of the species, like 

 the Nostochinece, impart a peculiar tint to large masses of 

 water, according as their prevalent colour is green or purple. 

 Phenomena of this kind have been observed in Switzerland 

 and Scotland.* 



118. It was once supposed that their endochromes were of a 

 totally different nature from those of Conferva^ consisting 

 merely of circular discs, filling up a common tube, and finally 

 expelled from it. There is, however, no doubt that they are 

 of the same nature as in other allied Algse ; that each is con-r 

 tained in a distinct sac ; and that multiplication takes place in the 



* See Lynghya Prolifica, t. 303 ; and De C'andollo, in M6moires de la 

 Soc. Pliys., &c., de Geneve, vol. iii. 

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