LECTURE XXI. 



RENEWAL OF ACTIVITY OF RESERVE-MATERIALS. FERMENTS, 

 DORMANT PERIODS. 



The constructive materials of the organs in the reservoirs of reserve-materials, as 

 well as those within other organs in their temporary conditions of rest, exist in forms 

 not suited for their immediate co-operation in growth. This is in part because they are 

 not soluble in the watery cell-sap, and are therefore incapable of being transported 

 — e. g. starch-grains, many aleurone grains, crystalloids, and slimy proteid substances. 

 It is above all necessary that these materials should diffuse from cell to cell and 

 travel from the places where they are deposited to those where they are used : 

 this is not possible in these conditions. 



Another point also comes into consideration here. Even cane-sugar, and similarly 

 inulin, though always dissolved in the cell-sap, only occur as reserve-materials, and 

 are not in a fit condition for direct employment in growth ; since when it is necessary 

 to make use of these matters in the growing germinal shoots, they are previously con- 

 verted into another chemical form, namely into a sugar which reduces cuprous oxide 

 in an alkaline solution, and which, neglecting further differences, we shall term 

 generally glucose. 



Since now cane-sugar, inulin, and to a certain extent even dissolved proteids, 

 occur in a transportable condition, and more or less capable of diffusion, it must in 

 this case be not simply a matter of making them capable of diffusion, but we may 

 assume that the chemical alteration also serves to render them in a condition 

 in which they are suited for direct employment in growth. In these changes of 

 the reserve-materials, therefore, it is not simply a matter of making them soluble and 

 transportable, but evidently of also converting them into a form directly serviceable 

 for growth. 



We may perhaps shortly formulate the matter thus. The plastic substances 

 present two conditions : in the one condition they appear passive, inactive, dormant, 

 whether in the solid or in the dissolved form ; in the other they are not only always 

 dissolved and movable, but are also in such a condition that they can directly take 

 part in the nutrition of growing cells. In this state they appear active, in contrast to 

 their passive condition in the reservoirs of reserve-materials. 



In both animal and vegetable organisms, organic compounds of peculiar kind are 

 produced, under the influence of which plastic materials arc converted from the passive 



