CELL-CONTENTS AND CELL-WALLS. 51 



(a) Make a strong aqueous solution of commercial asparagin, and 

 divide it into three portions. (1) Dissolve some copper sulphate in 

 water, and add dilute potash ; collect the precipitate on a filter, 

 and wash it with water. Add this precipitated copper hydroxide to 

 the asparagin solution asparagin (and other amides) gives a deep 

 blue colour ; evaporate the liquid down crystals of a copper com- 

 pound of the amide are formed. (2) Boil with dilute sulphuric acid 

 ammonia is formed ; add excess of magnesia and heat fumes of am- 

 monia are given off. (3) Add alcohol the asparagin is precipitated. 



(b) With a dry razor cut rather thick sections of Dahlia tuber, 

 mount in alcohol, and cover. On the evaporation of the alcohol, 

 rhombic plate-like crystals of asparagin are deposited on the 

 cover-glass and slide. Raise the cover, place on the section a 

 completely saturated solution of asparagin, and place the cover- 

 glass on again ; if the c^stals are really asparagin, instead of being 

 dissolved they will increase in size substances other than asparagin 

 would dissolve in the saturated asparagin solution just as they 

 would in water. In this way we can distinguish the asparagin 

 crystals from the deposits of inulin ( 77), which also occurs in the 

 Dahlia and is precipitated by alcohol. 



(c) The tyrosin in Dahlia tubers may be thus demonstrated : 

 (1) Keep sections mounted in glycerine for several days ; needle- 

 like crystals of tyrosin are deposited in radiating groups. (2) Place 

 a fairly thick slice of tuber in a dish of about the same size as itself, 

 and nearly cover it with alcohol ; the tyrosin crystals will appear 

 on the cut surface of the tuber. (3) Note that the tyrosin crystals 

 are coloured deep red by Milloii's reagent. (4) Tyrosin gives a 

 yellow colour when warmed with nitric acid, becoming orange on 

 addition of ammonia, (o) Place some of the crystals in a dry test- 

 tube, add a few drops of strong sulphuric acid, and place on a bath 

 at 100 for half an hour ; then add about 5 c.c. of water, neutralise 

 with barium carbonate, filter, and to the filtrate add two or three 

 drops of ferric chloride a blue or violet colour is given. 



(d) Cut sections of (1) dry seeds, (2) seedlings, of Lupin ; mount 

 in water, and test some for asparagin, others for proteins. If the 

 seedlings are preserved in alcohol for some weeks, sections mounted 

 in glycerine will often show large asparagin crystals ; on irrigation 

 with water the crystals are dissolved. 



Note that the dry seed contains no asparagin, but abundant 

 proteins. When the radicle is 1 to 3 cm. long, and the hypocotyl 

 2 to 5 mm. long, these organs contain some asparagin, but none is 

 present in the cotyledons. When the radicle is 5 or 6 cm. long, but 

 the cotyledons not yet expanded, the radicle and hypocotyl contain 

 larger quantities of asparagin, which is still absent from the coty- 

 ledons. In older seedlings, with expanded cotyledons, the latter, 

 as well as the other organs, still contain asparagin. As germination 

 advances and the plumule elongates, this organ is found to contain 

 asparagin, which gradually disappears from the other parts. 



