34 THE VICTORIAN NATURALIST. 



or locomotion of the whole plant ; secondly we may see in large 

 species of Closterium, Pleurotsenium, &c., the circulation or 

 rotation of the protoplasm ; this, however, is often obscured by 

 the parietal chloroplasts. Thirdly there may be seen, in species 

 of at least the two genera just mentioned, apical vacuoles, 

 containing colourless cell fluid, and in the fluid exceedingly 

 small particles of matter in violent agitation. These particles 

 are known as " dancing granules," and are described by Professor 

 West to be rhomboidal crystals of gypsum. They usually cluster 

 near the centre of the spherical vacuole, but I have noted in 

 experiments with Closterium ehrenbergii and Pleurotcenium 

 ehrenbergii that in whatever way the plant may be held there is a 

 tendency on the part of the granules to sink earthwards, thus 

 indicating geotropism, although this was less noticeable when 

 stimuli were administered. 



In a Pleurotsenium of above-named species, which I am 

 exhibiting, may be seen other than terminal vacuoles. These 

 will be seen to contain dense masses of the granules, so like a 

 compact swarm of bees in movement that the term " swarming 

 granules " is often applied. I take this to be an unhealthy sign, 

 having frequently noticed it as preceding decomposition of the 

 cell contents. It is not uncommon, but in the present case 

 has been produced under abnormal conditions — viz., change 

 of environment. The Desmids were taken from a large lagoon, 

 and have been kept some weeks in a small supply of water which 

 daily lessened by evaporation. 



The locomotion of Desmids has been much discussed lately. 

 West and West describe the results of their own and Stahl's 

 observations, which, in the case of a plant such as Closterium, 

 were as follows : — The plant, from a prone position, slowly raised 

 itself on one end, the free end passing through i8o° of arc, until 

 the plant again lay prone, but in a position its own length nearer 

 the objective point of its journey, and with ends reversed. The 

 process was repeated, and so the plant moved in steps equal to 

 its own length. " This," the authors remark, " is an exhibition of 

 periodical polarity, brought about by an alternation of positive and 

 negative heliotropism or geotropism, or a combination of both." My 

 own experiments showed this reversal of ends, in Desmid-length 

 steps towards the light, to occupy about half an hour at least, and 

 the time was much lengthened if any sort of obstruction interfered. 

 In the case of many longer periods, several abortive attempts to 

 turn over were made, the Desmid sinking back after each to the 

 old position, but I have observed, on more than one occasion, 

 that Closterium malinvernianum seemed to prefer progress 

 by attachment of one and the other end alternately, but 

 by keeping on its flat side, and moving by swinging round in 

 horizontal plane, while an obstruction to this method caused it to 



