vi HOW TO PREPARE AND EXAMINE SECTIONS 71 



pick out the thinnest. Mount in glycerine. Examine with the high 

 power of the hand -lens. Note 



(i) The mid-rib, which is the most prominent part of the section. In 

 the centre of this a vascular bundle will be seen, 

 (ii) The epidermis which covers the whole 

 surface of the leaf. 



(iii) The ground tissue which comes between 

 the lower epidermis and the upper. 



How to Use a Compound Microscope 



The following is a set of rules to direct the 

 student how to use the compound micro- 

 scope : 



(1) Before commencing to use the micro- 

 scope it must be examined to see if it is per- 

 fectly clean. If any mounting media or 

 reagents find their way on to the stage, clean 

 them off at once with a soft clean cloth. 



(2) To examine the lenses, the light must be 

 directed up through the tube by the mirror. 

 If the eye-piece be rotated, and specks of 

 dust move with it, they are on the lenses of the 

 eye-piece. The lenses must be unscrewed, and 

 the dust cleaned off with a soft silk rag. If the 



dust does not rotate with the eye-piece, it is on the objective, which must 

 be cleaned in the same way. If either glycerine or Canada balsam is 

 smeared on the objective, it must be cleaned by a jet of water directed 

 on to it from a wash-bottle and then be carefully dried. Canada 

 balsam is removed easily by alcohol or benzol. 



(3) To examine a specimen on a slide screw on the low power 

 objective, and move the mirror until the whole field is illuminated. 



FIG. 99. Transverse 

 section of stem and 

 prickle of Dog Rose. 

 (X 4 .) 



FIG. zoo. Transverse section of leaf of Rhododendron. ( X 8.) 



Then rack the tube down until it nearly touches the slide ; if the tube is 

 now racked up very slowly the object will come dimly into view. In 

 most cases a good view can be obtained with a low power without 

 using the finer adjustment, but if there is any difficulty the fine adjust- 

 ment can be used. 



