MOUNTING AND PEEPAEATION OF OBJECTS. 63 



It has been recommended to mount diatomacese 

 in bisulphide of carbon, as its high refractive index 

 makes their markings more distinct. We have as 

 yet had no experience of its efficacy in rendering 

 their details developable on a sensitised surface. 



Since the first discovery of the markings on the 

 diatom aceae their true nature has been the source of 

 endless strife, and is at the present moment in as 

 unsettled a condition as ever. I remember having 

 experienced immense delight many years ago, when 

 for the first time I perceived that the dots on some 

 of the coscinodisceae consisted of a coarse and fine 

 variety, and that I could reproduce exactly the same 

 appearance by placing two pieces of glass covered 

 with hemispherical elevations within two or three 

 inches of each other. Since then my ardour with 

 regard to the investigation of the structure of the 

 diatomaceae has cooled, and I have made no further 

 attempt to prove how far the foregoing experiment 

 is an explanation of their appearance. My belief is 

 that they are hemispherical tuberosities, in the 

 diatomaceae proper. Their markings possess little 

 interest now, since they are allowed to have no value 

 even as tests, for resolving power of objectives; in 

 fact the investigation of their structure has led to 

 such a mis-application of talent and waste of time, 

 that the majority of workers in science have handed 

 this department over to the amateur. 



Botanical preparations require considerable care 

 in their preparation, and as a rule are best examined 

 in the fresh state. A few, such as sections of stems, 



