252 Transactions. — Botany. 



effort." Many observers have recorded notes on this subject. Ealfs quotes 

 the following : — " It was impossible to determine whether the vague motions 

 of Closterium were voluntary or not" (Dalrymple) : — "I have seen Euas- 

 trum margaritiferum move quite distinctly" (Bailey) : — " Elles n'ont pas 

 un mouvement sensible sur le porte-objet du microscope" (Brebisson) — 

 contradictory assertions evidently. Mr. Archer (in Pritch. Inf., p. 5) says 

 that " the Desmidieas are seen to move. * * * * This phenomenon is 

 most notable in Closterium ; in others it is scarcely, in many not at all, 

 cognizable." The Bev. Mr. Osborne, in the Journ. of the Micros. Soc, ii., 

 235, attributes the movements of Closteria to cilia, but no other observer 

 seems to agree with his views. A friend of mine tells me that he has 

 frequently seen CI. lunula "rolling over and over." But none of these 

 statements appear to me to satisfactorily settle the Question whether the 

 Desmids do voluntarily travel, in any willed direction, as the Diatoms do, 

 or whether the movements observed may not have been due to some cur- 

 rents in the water or disturbing influences beyond the field of the micro- 

 scope at the moment. I venture, therefore, to give a few notes of the 

 motions observed by me in Cosmarium botrytis, motions which I believe 

 to have been perfectly " voluntary," and not due to any external in- 

 fluences. 



I had been observing the plant on a morning during the present spring, 

 and comparing it with some specimens in my English gatherings. The 

 specimen under observation was situated in the centre of my " field," in a 

 small clear space between a dead Pimiularia and a small speck of dirt. It 

 had been stationary for quite an hour, and there was no appearance during 

 that time of any " swarming" within it. The day was fine, and an even 

 full light came through the diaphragm. All at once I detected a com- 

 mencement of "swarming," quite faint at first; and when this had con- 

 tinued two or three minutes, I observed a slight oscillation of the frond. 

 By degrees the oscillation increased, and the Desrnid began clearly to move 

 from its place. Soon the motion increased, and the plant steadily worked 

 its way out between the Pimiularia and the dirt, not gliding straight-forward 

 but jerking along, with a motion exactly like that of a man elbowing his 

 way through a crowd, pushing forward first one side and then the other. 

 It was clear that the Pimiularia could not produce any effect on it, as it 

 was dead ; and I carefully looked to see whether anything in its neigh- 

 bourhood could have set a current in motion, but found nothing. In about 

 ten minutes the Cosmarium had jerked or elbowed itself out into the open 

 water, and still continued its journey towards the apparent lower edge of the 

 slide. Five minutes after, the " swarming " somewhat increased, as did 

 also the oscillation ; and the plant then stopped and began (also in jerks) 



