FERMENTS. 87 



variety, but the different clusters will usually be of different 

 varieties. Each of these has evidently developed from a 

 single germ or spore which has happened to fall at that spot. 

 By what means do these bacteria appropriate the starch of the 

 potato to their nutrition ? This material is not, as we know, 

 in a state fitted for the nutrition of these organisms; nor, 

 even in a condition in which it can be taken up by osmotic 

 action. The starch must be digested before it can be appro- 

 priated. That this digestion really takes place may easily 

 be shown. If we prepare the potato as above described, 

 watch it until the micro-organisms have grown to a greater 

 extent until they have spread over the surface and the 

 little clusters have coalesced with each other then cut a 

 very thin slice from the surface, and submit this to the chem- 

 ical test, we will find that a part of the starch has been 

 changed into glucose, or some form of sugar. This change 

 is the usual first act in digestion by plants, when starch is 

 the substance acted upon, and is the primary digestion per- 

 formed by the diastase, or soluble ferment secreted by these 

 organisms for the preparation of their food. This change 

 goes on very rapidly, and the greater part of the sugar formed 

 is at once appropriated to the nutrition of the organisms, and 

 its molecular form again changed. In the earlier stages of 

 the process or growth, it is probable that the sugar formed is 

 very nearly all used as fast as formed, but when the growth 

 becomes very luxuriant, there is a superabundant digestion 

 which permits us to find the traces of the sugar, which reveals 

 the manner in which the nutrition of the little plants is 

 brought about. 



This process will continue until every particle of the starch 

 has been remoleculized. But this is only one of the series of 

 remoleculizations which take place. The starch is converted 

 into sugar, the sugar into tissue of the growing plants, and 



