9 o 



They are very active in germinating seeds, e.g., in the process 

 of malting barley. The ferment present in malt was first dis- 

 covered and was called diastase, and hence all unorganized 

 ferments which convert starch into sugar are called diastatic. 

 But how does the sugar in solution pass through the protoplasm 

 of the cells where it is transformed ? for this offers a considerable 

 resistance to the passage of substances through it. In the 

 case of the beet-root, quoted in an early part of this paper, we 

 saw that the cane sugar present in the cell- sap did not pass 

 through the protoplasm and escape from the cells into the 

 surrounding water in which the section was immersed, even 

 when the cells were allowed to remain there for some con- 

 siderable time. To this question it is, unfortunately, at present 

 impossible to give a definite answer. Possibly the sugar at 

 once undergoes a change into a substance which will pass by 

 diffusion through the protoplasm more readily than it can itself 

 do — i.e., into some form of vegetable acid ; or perhaps the 

 sugar exists under these conditions of formation in a form dif- 

 ferent from, and more diffusible than, that in which it is met with 

 after it has lain for a long period in the stores or reservoirs 

 of the plant. There is no doubt whatever that it does pass in 

 some form or other from the leaves to the other parts of the 

 plant. If we assume either that it is directly converted into a 

 very diffusible form of sugar, or indirectly into some diffusible 

 substance, such as a vegetable acid, we have the key to the 

 whole distribution of the sugar solution in the plant. Now it 

 is the movement of this sugar solution which has been long 

 known as the descending current of the elaborated sap. It was 

 formerly said that its course was a downward one, through 

 that portion of the growing wood in ordinary forest trees (Dico- 

 tyledons) which we know as the cambium ; a zone of ordinary 

 parenchyma cells capable of division, and from which the 

 annual additions take place to the exterior of the wood proper 

 which lies internally to it, and to the interior of what is known 

 as the inner or bast layer of the bark, which lies externally to 

 it ; and also that it passed through certain vessels in this bast 

 layer as well. 



