28 PRACTICAL BOTANY 



is embedded in the peripheral protoplasm, while the whole 

 cell-cavity is occupied by a large vacuole. 



Examining the nucleus more closely there may be dis- 

 tinguished 



a. Deeply stained fibrillae, forming apparently a convoluted 

 coil, or a reticulum : this is the chromatin. 



b. An unstained matrix in which the fibrillae are embedded 

 the achromatin. 



Pith of a very young shoot of the Elder will also serve as 

 good material for these observations ; the young shoot should 

 be treated as above directed, and longitudinal sections will 

 afford similar results. As an alternative method of prepara- 

 tion, which has the advantage of simplicity, stain the sections 

 from material hardened in alcohol, with a solution of methyl 

 green in weak acetic acid, wash with weak acetic acid, and 

 mount in dilute glycerine : the nucleus only is distinctly stained 

 in this case, but the results are as a whole less satisfactory than 

 when the former method is used. 



III. Starch. 



a. Scrape the freshly-cut surface of a Potato tuber lightly 

 with a knife, and mount a small quantity of the scrapings in 

 water : examine first with a low, and then under a high power, 

 and observe scattered through the water a large number of 

 somewhat ovoid, colourless, bright-looking, i.e. highly refractive 

 bodies: these are starch-grains; near to one end, which is 

 usually slightly pointed, is a round clear spot, the hilum. The 

 grain will show a stratified structure : the layers of stratifica- 

 tion near the hilum are almost circular and concentric ; the 

 more external layers are excentric and elliptical, and are wider 

 on the side further from the hilum ; many of them between the 

 hilum and the broader end of the grain are incomplete ; hence 

 the layers are more numerous between the hilum and the broad 

 end than between the hilum and the pointed end of the grain. 



Here and there may be seen a compound grain, consisting 

 of two small grains in contact by their broad ends, and in- 

 vested by several layers common to both. 



b. Sections should also be cut from the Potato so as to show 

 the starch-grains in situ in the cells. The razor should be 



