MICROSCOPIC WONDERS 13 



Most beautiful colour effects are often obtained uninten- 

 tionally. The light is decomposed by the surface of the 

 frustules, and the cases are seen to be iridescent. A diatom 

 slide usually shows similar effects. 



Desmids resemble diatoms in the fact that they are single- 

 celled plants, But they have not the same wish, or perhaps 

 power, to build cases. But although lacking in this respect 

 yet they are most beautiful little objects, and any time spent 

 in their study is amply repaid. 



" Minute green plants " is perhaps the best description one 

 could give of them, for they contain chlorophyll, the green 

 colouring matter which we know so well in the higher plants. 

 And, as if aware of this fact, Desmids in fine weather are found 

 on the surface of the pond, forming a green film, whilst should 

 the weather be less bright they retire to the bottom, chloro- 

 phyll being essential in the decomposition of carbon dioxide 

 for the production of sugar and starch in the presence of sun- 

 light. 



During our usual fine hot summer weather, so characteristic 

 of our climate, these little plants appear in such large numbers 

 as to make the water appear green. 



Desmids are of all shapes, partly due to the fact that their 

 method of reproduction leads to great alterations in their 

 " physique," and partly due to the large number of species that 

 are in existence. 



Perhaps, if one asked the mycologist what he found interest- 

 ing in Desmids, he would reply, the study of "Cyclosis." 

 Cyclosis is the movement of protoplasm, and this may be most 

 easily studied under the microscope. 



But to the average person their methods of reproduction 

 are probably of more interest. 



The Desmid, when the instinct prompts it, gradually divides 

 the protoplasm and leaves a vacant space in the centre : a break 

 occurs and two Desmids result. This is not the only way that 

 Desmids increase. The other method is sexual, the former 

 asexual (fission). 



In the sexual method, known as conjugation, two Desmids 

 meet, the cell contents mix, and a spore is formed. This 

 spore then forms several Desmids of the same species. 



Closterium lunula is one of the most interesting, being 

 comparatively common, and especially easy to study. 



The phenomenon of Cyclosis can be easily followed. 



Another Desmid of peculiar interest is Cosmarium botrytis. 



Cosmarium botritis is noticeable for having on its surface 

 many nobbles ; these are arranged in rows. The Desmid is 



