174 LECTURE X. 



Lupins, that whereas peptone was abundant in the coty- 

 ledons of seedlings a week old, it was not present in any 

 other part. Seedlings, it is well known, contain considerable 

 quantities of amides, and the presence of these can only be 

 accounted for by regarding them as having been derived 

 from the reserve-proteids of the seed. It is then in the form 

 of amides that nitrogenous organic substance is supplied to 

 the seedling. All the various crystallisable nitrogenous or- 

 ganic substances which have been already mentioned are 

 to be found in germinating seeds, but they are present in 

 various proportions in different seeds. For example, Vetch- 

 seeds contain principally asparagin and leucin, together with 

 small quantities of glutamin and ty rosin (von Gorup-Besanez): 

 Pumpkin-seeds contain principally glutamin and asparagin, 

 with some tyrosin (Schulze and Barbieri). 



The effect of the absorption of these substances by the 

 embryo is that the cell-sap of the cells of its ground-tissue 

 become '.charged with them, for the supply is much more 

 rapid than the consumption in the formation of proteid ; 

 consequently the seedling soon comes to contain a larger 

 percentage of them than does the organ in which they are 

 being formed. If the seedling is growing under favourable 

 conditions these substances gradually diminish in quantity 

 and finally disappear, and this is accompanied by an increase 

 in the amount of proteid contained in the seedling. 



The nature of these conditions has been clearly made out 

 by Pfeffer. He found that Lupin-seedlings grown in the dark 

 contained a very large quantity of asparagin so long as they 

 continued to live, but that if they were exposed to light the 

 asparagin gradually diminished. But he ascertained further 

 that mere exposure to light is not the cause of this, since the 

 asparagin did not diminish in seedlings exposed to light 

 in an atmosphere which contained no carbon dioxide. The 

 disappearance of the asparagin depended therefore upon con- 

 ditions which were essential to the formation of non-nitro- 

 genous organic substances by the seedlings. The accumu- 

 lation of the asparagin depended upon the absence of a 

 supply of appropriate non-nitrogenous substance with which 



