76 CELL-CONTENTS AND CELL-WALLS. 



drops of oil are left on the slide. Examine with the 

 microscope; on focussing down, note that the dark- 

 looking ring around each drop becomes bright compare 

 with air bubbles, the dark ring around which simply 

 becomes broader on focussing down. 



(d) Pound up dry oily seeds (e.g. Sunflower, Linseed, 

 Castor Oil, Brazil Nut remove the coats from the larger 

 seeds) between folds of blotting-paper, and note the greasy 

 stain produced ; this dissolves in ether. Castor Oil and 

 Brazil Nut seeds are so rich in oil that the oil drops are 

 readily seen on cutting across the seed with a heated knife. 



(e) Place drops of various oils on a series of slides. In 

 each case add a drop of 1 per cent, osmic acid ; the oil is 

 coloured brown or black. 



(/) Examine commercial ground Almonds, a rather 

 greasy powder, and apply to it the tests for oils and for 

 proteins. 



(</) Cut sections of oily seeds, e.g. Castor Oil, Almond, 

 Brazil Nut, Sunflower, Walnut. (1) Mount in water, and 

 note the bright-looking oil drops, both in the cells and in 

 the water. (2) Mount dry-cut sections in a mixture of 

 equal parts ether and absolute alcohol ; the oil drops are 

 dissolved, but separate out again 011 letting the solution 

 evaporate. (3) Treat a section with 1 per cent, osmic 

 acid ; the oil drops become blackened. (4) Treat a 

 section with alkannin solution (see Appendix) ; this stains 

 the oil drops red, but an hour or more may be required. 

 It is often better to cut a section of dry alkanna root and 

 lay it on the section. In the case of Castor Oil, since the 

 oil is soluble in alcohol, it is advisable (unless the dry 

 alkanna root is used) to mix the alkanna tincture with an 

 equal volume of glycerine, and to examine the section in 

 glycerine. 



(h) Ethereal oils may be examined in sections cut with a dry 

 razor from fresh material, such as Orange rind, fruits of Um- 

 bellifers, etc. Note that these oils are stained by osmic acid and 

 by alkannin, are soluble in ordinary alcohol, and being volatile 

 disappear on being warmed: 



