24O PART III. VEGETABLE PHYSIOLOGY. 



tion, the latter process cannot be directly observed. In under- 

 going solution, the starch is changed into sugar, which, in its 

 various forms, is a highly diffusible substance. It may thus be 

 conveyed to parts very remote from its place of formation. The 

 transformation is brought about by the agency of diastase, or 

 some similar unorganized ferment. 



In the form of sugar, it may be conveyed to growing parts 

 and applied to the construction of tissues, or it may be carried to 

 various parts of the plant, as seeds, tubers, etc., and laid by as 

 reserve material. In this case it is sometimes stored as sugar, 

 for example, in the Sugar Beet; sometimes it is laid up in the 

 form of cellulose, as in the Ivory Palm and Nux Vomica seed ; 

 and sometimes it first goes to the formation of protoplasm, and 

 then of reserve proteid material, such as aleurone grains, etc. ; 

 but it is more commonly either re-converted into starch, or else 

 stored in the form of fixed oil. 



When starch and oil are to be conveyed from the tissues 

 where they are held in reserve to growing parts, they are again 

 brought into solution in the form of sugar, or some other soluble 

 carbo-hydrate, by the agency of an unorganized ferment. 



The transfer of proteid materials also takes place by their 

 conversion into compounds which are more readily diffusible, 

 such for instance as the amides, asparagin, glutamin, leucin, etc. 

 Doubtless their transfer, both to the place of storage and from it, 

 to the parts where they are required for use, is accomplished 

 chiefly in this way. 



Destructive Metabolism. At the same time that the con- 

 structive work of the plant goes on, there proceeds also a work 

 of disintegration and destruction. In the economy of the organ- 

 ism, life and death go hand in hand. The oxidation and conse- 

 quent breaking down of certain organized structures is a source 

 of energy which the plant uses in the work of construction. If 

 the constructive processes are in excess of the destructive ones, 

 there is growth ; if the latter are in excess of the former, the 

 whole organism soon dies. Every plant has its period of growth, 

 when the life-forces aie in the ascendant ; its period of maturity, 

 when repair and waste are nearly evenly balanced ; and its period 

 of decline, when the destructive forces gain the ascendancy. 



The highly organized structures that constitute the tissues of 



