446 MANUAL OF BOTANY 



The peptones dialyse with far greater ease than the albumoses. 

 They do not occur very plentifully in plants, and are probably 

 formed in them only from the decomposition of the more stable 

 forms of globulin and albumin. Some of the albumoses occur in 

 certain seeds in association with some of the globulins. 



By the action of peculiar secretions of the protoplasm, be- 

 longing to the bodies known as enzymes or unorganised ferments, 

 the globulins and albumins can be decomposed, with formation 

 successively of albumoses, peptones, and amides such as 

 asparagin and leuoin. 



It has been considered by some botanists that the sieve-tubes 

 or their companion cells are the places where the construction 

 of proteid is completed, only the amides being formed in the 

 leaves. It is, however, possible that this construction is, like 

 that of the deposition of starch in the chloroplastid, rather the 

 expression of the temporary deposit of proteid in those cells at 

 the expense of the surplus formation, which, not being needed 

 in the cells of the mesophyU, is converted into amides and so 

 transported from the leaf. A certain amount of proteid can be 

 extracted from the living cells which are the seat of the original 

 anabolic processes. 



The importance of the inorganic salts which do not enter 

 into the composition of the living plant-substance is very im- 

 perfectly understood. Potassium is apparently necessary for 

 the construction of carbohydrate matter by the chloroplastids. 

 It is generally absorbed in combination with sulphuric, nitric, 

 and hydrochloric acids, and can be found in the plant in com- 

 bination with organic acids such as tartaric, oxalic, and malic. 

 It is generally found in quantity in places where starch and sugar 

 are stored. 



Calcium and magnesium are absorbed in similar combina- 

 tions, but their fmiction has not been ascertained. The former 

 appears to be concerned in the transport of carbohydrates from 

 place to place. Both are of service in neutraUsing such acids 

 as oxalic, the presence of which in quantity is deleterious. V\'e 

 frequently find in cells, and in some cell-walls, crystals of oxalate 

 of calcium. 



The importance of iron has been pointed out in connection 

 with the action of the chlorophyll. 



Most of the other elements absorbed seem to be without 

 effect on the metabolic processes. 



