72 BOTANY FOR BEGINNERS CHAP. 



With a high power the method of finding the focus is the same, 

 only greater care is required. If the objective is used, it can be 

 racked down until the image of the objective appears to meet the 

 objective when the specimen is nearly in focus. If the tube is gently 

 racked away from the slide it will come into view, and with the finer 

 adjustment the focus can be found. 



The pupil must on no account rack the tube towards the object at the 

 same time he is looking down it. If this is done the object may be 

 missed and the objective may be forced through the slide. The section 

 may in this way be damaged and the lens ruined. The best way is to 

 look at the objective until it is nearly close to the object, and then, 

 while looking down the tube, rack it away until the object becomes clear. 



(4) An object should always be examined with the low power first, 

 and after all possible detail has been made out with this, the high power 

 can be used. 



(5) A high power must never be used unless the object is covered 

 with a cover-glass. This prevents the mounting media from touching 

 the objective. 



(6) Drawings should always be made of the objects examined. This 

 practice compels attention to details, and tends to produce the habit of 

 close observation. In drawing, a fine pointed pencil should be used, 

 and the drawings made either on good cartridge paper or Bristol board. 

 The drawings should always be made to scale. 



SUMMARY. 



Sections of a plant can oe made in three directions. If the section of 

 the stem is made at right angles to its long axis it is called a transverse 

 section. When the section is made in the direction of the long axis of 

 the stem and passes through the organic centre, it is a radial longi 

 tudinal section. If the section passes lengthwise through the stem but 

 does not pass through the organic centre, it is said to be a tangential 

 longitudinal section. 



Mounting Specimens. Fresh specimens can be mounted in water, 

 and material which has been preserved in alcohol must be mounted in 

 either alcohol or glycerine. Sections must be kept wet to prevent air 

 bubbles from forming. Cleanliness is necessary if good work is to be 

 done. 



Hand-Lens. A hand-lens is a piece of glass which possesses the 

 property of magnifying objects, and is mounted in wood, horn, or metal 

 for protection and use. To use such a lens it is necessary to hold it 

 close to the eye and to bring the object into such a position that it can 

 best be seen. 



Cells. Plants are built up of elements which receive the name of 

 cells. A cell is surrounded with a cell-wall, and contains protoplasm. 



Tissues are formed by the union of a number of cells. There are 

 three kinds of tissues ; they are- 

 Epidermal tissue ; 

 Vascular tissue ; 

 Ground tissue. 



