28 The Use of a Simple Microscope. 



ledge, diligent use of the compound microscope is indispensable, 

 accompanied by some work on histology or vegetable physiology 

 as a guide to the mode of investigation. 



Diseases are also supposed to be produced by fungi, such as 

 mildew, rust, &c., but these growths are rather indicative of dis- 

 ease elsewhere. When the normal condition of the cell struc- 

 ture, of the root fibres, leaf-cells, and other parts of the plant are 

 known, the mycelium of these fungi may be recognised and 

 sometimes traced all through the structure. To comprehend 

 the nature and arrangement of these fungous pests of vegetable 

 life every part of the plant should be carefully examined for 

 their presence. 



The structure of the leaves also bears a marked significance as to 

 the mode of treatment plants ought to receive ; the hairs and glands 

 upon their surface, the stomata on one or both sides, are all con- 

 nected with the laboratory within the substance, and have their 

 respective functions to perform, any cessation of which becomes 

 the precursor of disease. Portions of the upper or under skin of 

 the leaf may be stripped off with a sharp knife and placed wet 

 between glasses so as to be ready for examination. The internal 

 structure of the leaf is best seen by taking a very thin section 

 by means of a razor across the thickness of the leaf, and thus 

 getting an edgewise view of it and the hairs, &c., which are 

 connected with it. Sections made with a sharp razor may be 

 taken from all parts of the plant so as to afford a considerable 

 amount of knowledge of its peculiar structure. 



Dry and hard seeds, such as peas and beans, «Scc., after being 

 thoroughly softened in water, may likewise have thin slices 

 shaved off in the same manner. For the method of preserving 

 these and other substances the reader is referred to the before- 

 mentioned manual of Mr. Davies on mounting, »S:c. 



All small seeds may be preserved in a very simple manner 

 when required only for reference. Take a strip of any common 

 card, or stiff paper, cut to 1 inch wide and 3 inches long, which 

 is the standard size of microscopic object-slides. In the centre 

 of this put a little thick gum, or thin flour-paste, and drop on it 

 a heap of the clean dry seeds, and after a few minutes shake off 

 all that are loose ; put aside till thoroughly dry, and, if preserved 

 from dust and damp, they may be kept for years. A collection 

 should be made of the seeds of all common weeds, but more 

 especially of those that are particularly obnoxious or injurious to 

 crops or pasture. 



All materials such as wool, hair, vegetable fibres, starch, 

 pollen, very minute seeds, or dust of any kind, if required dry, 

 may lie preserved between two pieces of glass fastened together 

 by paper pasted upon them ; but these are more commonly first 



