PREPARATION AND MANIPULATION OF SECTIONS. 



27 



The section selected should be observed in glycerine, either 

 concentrated or diluted with about one-third distilled water. 

 Pure water should not be used, as it quickly sets up phenomena 

 of disorganisation in the ground substance of the cells. The 

 transfer of the section from the razor to the glass-slide is best 

 made with a fine camel-hair brush. The section is removed by 

 pressing the brush upon it and sliding it off from the blade. If 

 it adheres to a sufficiently broad surface of the brush, " curling" 

 of the section will be prevented ; curling occurs very easily, on 

 the other hand, if the section is taken directly by its edge with 

 the tweezers and so transferred. The section adhering to the 

 brush is immersed flat in the drop on the glass-slide, and the 

 brush withdrawn sideways with a simultaneous twisting move- 

 ment. If it is desired to turn a section over when on the object- 

 slide, press the brush down on the object-slide so that it is in 

 contact with the edge of the section, and then begin to turn it 

 over away from the section. In this way the section will be very 

 easily drawn upon the upper surface of the brush, and can then 

 be turned over with it. Other similar "dodges" will soon be 

 acquired in practice. After every time of use the brush must be 

 most carefully washed in water. Very small or stiff sections can 

 be readily lifted on a needle. Flattened needles, slightly bent, 

 can also be used with advantage. 



The Pea. The Cell and its Enclosures. Examine the section 

 of pea first with a low power 

 to get a general idea of its 

 nature, and to select the 

 best place for study; then 

 change to a stronger power. 

 It proves to be a tissue 

 composed of rounded cells. 

 At the places where three 

 such cells adjoin one another 

 a triangular intercellular 

 space (/) filled with air is 

 present. The air appears 

 black, like the edge of the 



air bubbles previously de- FlG . 1L -From the cotyledons of the Pea. *. 



SCl'ibed ; here it naturally ce H wall ; i< intercellular space ; am, starch ; al, 



, . aleurone grains ; />, ground substance ; n, nuc- 



must SHOW the form Of the leus. This last is shown by acetic methyl green 



space, since it fills it. The ( x 240)> 



