THIRD SECTION. 

 Metabolic Processes in the Plant. 



I. THE BEHAVIOUR OF NITROGENOUS COMPOUNDS. 



93. The Proteids Which can be Isolated from Plant Structures. 



WE shall here entirely disregard the organised protoplasmic 

 structures of plant-cells, already dealt with in 46, and confine 

 ourselves to showing that various proteids are to be met with 

 in the vegetable organism. 



If we grind wheat or barley fruits to powder (about 25 gr.), 

 and leave this in water for some time, we can obtain by filtration 

 a clear liquid in which the presence of albumin may be detected. 

 On heating this fluid the proteid coagulates, and separates out as 

 a clot. If we filter and warm the juice expressed from crushed 

 fruits {e.g. grapes), we shall again obtain a coagulum of pro- 

 teid. 



To the second great group of vegetable proteids, the vegetable 

 caseins, belong the legumin of beans, peas, etc., the conglutin of 

 lupins, and the glutin-casein of grasses. We select for somewhat 

 careful investigation conglutin. Seeds of Lupinus luteus are 

 ground up in a small hand mill, the powder (about 25 gr.) is 

 treated with distilled water, and to the mixture is added potash 

 solution until the fluid has a slight alkaline reaction. The remains 

 of the seeds are separated by means of a hair-sieve from the 

 conglutin- containing fluid, which is then filtered and very slightly 

 acidified with Acetic acid. The precipitated conglutin is collected 

 on a filter, and washed with water. Conglutin is insoluble in 

 water. If, however, we suspend some conglutin in water, and treat 

 it with Phosphoric, Acetic or Citric acid, or a solution of Sodium 

 phosphate (Na 2 H P 4 ), it dissolves. 1 



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