sect. II PHYSIOLOGY 203 



first become dissolved and form soluble amides. They are in this 

 form transferred to places where in combination with carbohydrates 

 and mineral acids they are used anew in the formation of albumen. 



Besides asparagin, there are still other but less widely distributed amides found 

 in plants, as leucix, tyrosix (which, like asparagin, will crystallise out on treat- 

 ment with alcohol as glistening sphaerites), glutamix (in the Pumpkin), betain 

 (in the Turnip), also allaxtoix, etc. 



In addition to the transfer of nitrogenous constructive material 

 through the parenchymatous tissues, the long-distance transport of 

 the ready-formed albuminous substances seems rather to take 

 place through the open sieve-tubes of the bast. It appears to be in the 

 sieve-tubes, which contain, during life, albuminous substances, starch 

 grains, and drops of oil, that the conduction of organic substances is 

 effected from the leaves to the roots. In fact, it was long ago con- 

 cluded that the increased thickening of the cortical layers observed just 

 above wounds made by ringing trees, was due to the interruption and 

 detention of a flow of nourishing sap through the bast towards the 

 roots. 



The transfer of the carbohydrates through unbroken cell walls to 

 the various points of consumption can only be accomplished when they 

 are in solution. In case they are not alread}' dissolved in the cell sap, 

 in the form of glucose, maltose, sugar, or inulin, they must first be 

 converted into soluble substances. This is of the highest importance 

 for 'the transfer and utilisation of starch and reserve cellulose. They 

 are converted by the influence of diastase into glucose or maltose. 

 Diastase belongs to those peculiarly acting substances termed UN- 

 ORGANISED ferments or ENZYMES, which possess the remarkable 

 power of decomposing or transforming certain organic compounds 

 without themselves becoming changed or consumed in the process. 

 By virtue of this property they are enabled to transform unlimited 

 quantities of certain substances. The best known of the unorganised 

 ferments are diastase, which converts starch into maltose, invertin, 

 emulsin, myrosin, as well as the peptonising ferments in insecti- 

 vorous plants and in the latex of various plants. 



These ferments are proteinaceous substances, which in many of their chemical 

 reactions resemble living protoplasm, but with which they must not be eon- 

 fused. Their power of exciting fermentation is not due to any vital property ; 

 they are simply chemical substances, and like them, when in solution, may be 

 precipitated, etc., without losing any of their active principles. Diastase, for 

 example, may be extracted from germinating barley seeds by water or glycerine. 

 After it has been precipitated by means of alcohol and dried to a powder, it may 

 again be dissolved in water, and will still be in a condition to transform enormous 

 quantities of starch, especially if in the form of paste, into sugar. 



Other substances similar to diastase, and also capable of dissolving starch, 

 are widely distributed throughout the vegetable kingdom, and are classed together 

 as diastatic ferments. They are especially abundant in starchy germinating seeds, 



