2l8 PART II. — VEGETABLE HISTOLOGY. 



of rendering important service, but which, if too much depended upon, tends 

 more to foster slavish copying than to develop either artistic skill or the power 

 of careful and accurate observation. The first efforts of the student at drawing 

 had better, therefore, be undertaken without its aid. He should begin with 

 simple structures, such as single cells, starch grains, etc., and after he has 

 acquired a degree of skill, proceed to more complex structures. The apparent 

 dimensions of an object may readily be transferred to paper by means of a pair 

 of compasses in the manner already suggested. Further aid in getting the rela- 

 tive dimensions of different parts and in locating different points in the struc- 

 ture, may be obtained by a judicious use of the eye-piece micrometer. Of still 

 greater advantage for the same purposes, however, is an eye-piece scale, ruled 

 in equal squares with rather strong black lines and not too near together. 



In using the camera lucida, it is of importance that the drawing-paper and 

 the field of the microscope be nearly equally illuminated, otherwise the pencil- 

 point and the object to be delineated cannot be seen with equal distinctness, 

 and the lines of the structure, therefore, cannot be accurately followed. The 

 outlines of the object had best be traced with a fine-pointed lead-pencil. 

 Faber's or Hardtmuth's HHH drawing pencils are excellent for the purpose. 

 The most convenient way to give the pencil a fine point is by means of a rather 

 fine flat file. The tracing should be made on fine white cardboard, or on the 

 smoother qualities of Whatman's drawing paper. The camera will seldom be 

 used except to draw outlines and locate important points in the structure. The 

 position in which it must be used makes the filling in of details and finishing by 

 means of it too tedious and troublesome. 



Drawings designed merely as a record of observations, or which are to be 

 copied by the wood-engraver, may be finished in lead-pencil, but those which 

 are to be copied by any of the photographic processes should be drawn with a 

 pen in the blackest of black ink. 



In his earlier attempts at drawing microscopic objects, the student would do 

 well to use as models the admirable drawings found in Sach's Physiology of 

 Plants and in Fliickiger's Pharmacognosy. 



GENERAL DIRECTIONS FOR MICROSCOPIC WORK. 



1. Acquaint yourself thoroughly with the mechanism of the microscope 

 you are to use. 



2. Observe great care in the removing and putting on of objectives, so as 

 not to drop them, for they are delicately constructed and liable to injury. The 

 eye-pieces and eye-piece micrometer should also be handled with care. 



3. Observe care in focussing, particularly when high powers are used, so 

 as not to run the objective down against the slide and endanger either the 

 cover-glass or the objective itself. Be sure also that you focus the microscope 

 accurately, otherwise the structure of the object will not be distinctly seen. 



4. Give due attention to the adjustment ot the reflecting mirror, so as to 

 secure the most favorable illumination of the object. Much of your success in 



