SUGAR 221 



in very slightly diluted tincture of iodine, and mount in pure 

 glycerine : examine under a high power, and observe 



1. The cells of the usual parenchymatous type, with protoplasm 

 and nucleus. 



2. Numerous spherical bodies, usually aggregated round the 

 nucleus : in some cells these will stain blue (starch), with a small 

 yellowish body attached which is the leukoplast ; in other cells, 

 which were nearer the outer surface of the tuber, the bodies will 

 stain uniformly yellowish brown : these are the young leilko- 

 plasts which have not yet formed starch. 



The material which has been found best suited for the observa- 

 tion of leukoplasts is the young tuber of the Orchid Phajus 

 grandifolius (Bletia TanJcervillice), but it is not to be expected 

 that this will be within the reach of all. Here the leukoplast is 

 of large size, and rod-like form : this material may be treated 

 similarly to the Potato, or a method recommended by Strasburger 

 may be adopted, viz., to cut the sections and fix and stain them with 

 picro-nigrosin, which colours the leukoplasts a steel-blue tint. 



II. For inulin and its reactions see p. 119. 



III. Cellulose occurs as a reserve in the endosperm 

 of the Date, and other Palms : the appearance of these 

 has been described on p. 38, and the sections should be 

 cut and the reactions noted. Thickened cell-walls will 

 also be found in sections of the cotyledons of Lupinus. 



IV. Sugars. 



(a) Grape-sugar. Cut a transverse section of a ripe 

 grape, of such thickness that some cells at least shall 

 be uninjured : mount in water, and observe under a 

 low power the transparent parenchymatous pulp, con- 

 sisting of cells with thin walls, very sparing contents, 

 and large central vacuole. 



Treat for a few minutes with a relatively large bulk 

 of alcohol in a watch-glass : on re-examining, numerous 

 crystals will now be seen in the cells. 



