USE OF THE SIMPLE MICROSCOPE. 209 



In order to prepare or to dissect with the compound micro- 

 scope itself, what is called an "erecting eye-piece" can be 

 used in the place of the ordinary eye-piece of the microscope. 

 This " erecting " eye-piece reverses the image of the object; and 

 as, in a compound microscope, the image is normally upside 

 down, it is thus rectified. It is, however, quite possible, though 

 to a beginner very difficult, to dissect, etc., with the ordinary 

 compound microscope. With practice one comes to realise that 

 every movement is reversed, and to govern the movements 

 accordingly. The low powers can then be freely used for dis- 

 section and preparation. In dissection, etc., with the compound- 

 microscope it is of advantage to have two blocks of wood of 

 suitable size, which can be placed on either side of the stage, and 

 will serve to support the hands. 



Whatever instrument is used the method is the same. Place 

 the preparation, uncovered, on the stage of the microscope, and 

 after proper adjustment of the mirror, and focussing, take in each 

 hand a needle fixed in a holder (see Introduction), steady the 

 ^hands on the rests, bring the points of the needles into the 

 optical axis of the instrument, and endeavour to see both simul- 

 taneously in the field of view of the microscope. This will soon 

 be successfully accomplished, and then by means of a few experi- 

 mental attempts one can learn how to make the necessary slight 

 movements with the needles. 



Let us now clean our preparation in this way, and then 

 proceed with its examination. The leaves of Hipp ur is grow in 

 whorls of many members ; under the youngest whorl but one 

 the nodes of the stem begin to be marked as horizontal denser 

 plates (diaphragms) of tissue, above and below which, in the 

 cortex of the stem, proceed the air-passages. These air-passages, 

 which extend from one nodal diaphragm to the other, become 

 larger in proportion as the stern enlarges. The internodes 

 elongate very rapidly and symmetrically, and in the same pro- 

 portion their thickness also increases. Under somewhere about 

 the fourth youngest leaf- whorl the formation of vascular tracheides 

 in the stem begins. These are very beautifully seen after the 

 addition of a little potash. These tracheides traverse the long 

 axis of the stem ; they appertain to a vascular bundle which 

 grows acropetally, and ends above with individual annular trache- 

 ides. In about the tenth to the twelfth node the vascular 



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