MICROSCOPIC OBJECTS. 83 



men, similar to his slides of recent woods. By this 

 means a correct idea of the form of the organs can be 

 obtained. — Magnifymg power 50 to 150 diameters. 



Fungi. — This tribe of aerial Cryptogamous plants — of 

 which the Mushroom fAgaricus campestrisj and the 

 Truffle (Tuber CihariumJ are the only wholesome species 

 — contains numerous genera, the study of whose produc- 

 tion is important to man from their injurious effects upon 

 his food. The various kinds of mildew upon wheat and 

 vegetable substances are familiar examples of the minute 

 kinds of Fungi, all of which requu'e the aid of the micro- 

 scope, and in general very high magnifying powers, for 

 their investigation. 



Grasses. — ^The stems of many grasses and the husk 

 which envelopes the flowers and seeds, form excellent 

 microscopic objects, especially when silica enters into 

 their composition. The husk of the oat and of the wheat 

 has been mentioned before. 



Lichens — are an extensive order of Cryptogamous 

 plants, growing upon rocks, bark of trees, old palings* 

 &c., and indicate by their presence dry open situations, 

 while the Fungi are produced in damp places. 



Mosses. — Our knowledge of the structure of the Musci 

 is derived exclusively through the agency of the micro- 

 scope. They are supposed to be devoid of woody fibre 

 and vascular tissue. When a leaf is carefully examined, 

 the septa which divide the cells are found in some species 

 to take a spiral course. To observe this structure, pre- 

 viously soak the mpss in water, to expand the cells. In 



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