102 OF THE MARINE ALG.E. 



to lay such monstrous specimens between sheets of writing 

 paper, or to put them away in the herbarium cabinet. The 

 consequence is, that they are more or less exposed to the 

 action of the air, which is almost sure after a while to 

 impart to them a considerable amount of moisture. 



In examining this class of Algae it is necessary (if his 

 investigations are to be of any value) that' the student 

 should make himself acquainted with their anatomical 

 structure. In numerous cases this is by no means difficult, 

 on account of their transparent nature, which allows of 

 their whole inner structure and delicate cellular tissue 

 being examined at leisure under the microscope. In those 

 species, however, which are furnished with a thick leathery 

 frond and stem, it is requisite to cut fine sections, otherwise 

 their opacity effectually prevents any view of the form and 

 arrangement of the cells. [With regard to this part of the 

 subject I must refer the reader to works in which the 

 methods of preparing objects for the microscope are de- 

 scribed at length : as, for instance, c Davies' Preparation and 

 Mounting of Microscopic Objects,' where the whole matter 

 is thoroughly discussed. — Ed.] I will only observe here, that 

 the examples to be operated on had better be quite dry, 

 because in their wet state they are very apt to get torn 

 instead of being accurately cut, the cells coming apart and 

 hanging together in disorder. The section must be. placed 

 in water or spirits of wine, and left for a while to absorb the 

 fluid ; it is then fit for examination on a slide. 



The lime-producing Algae (by which I mean Corallina, 

 Jania, Acetabularia, Liagora, Melobesia, and similar genera.) 

 must not be submitted to the knife until the incrustation 

 has been entirely dissolved by means of an acid. 



It is often very difficult to detect the true structure of the 

 cell walls in the strictly gelatinous Algae, as also in many of 

 the Enteromorpha and some other families. The best plan 

 in such cases is to add a drop of a solution of chloride of 

 zinc and iodine to the fluid in which the section is im- 

 mersed on the slide. By this expedient a conspicuous blue 



