414 BOTANICAT. BIOLOGY. 



There is no part of the field of physiological botany which has yielded 

 results of more interest and importance than that which relates to the 

 action of ferments and fermentation ; and I could hardly give you a 

 better illustration of the purely biological method of treating it. I 

 believe that these results, wonderful and fascinating as they are, afford 

 but a faint indication of the range of those that are still to be accom- 

 plished. The subject is one of extreme intricacy, and it is not easy to 

 speak about it brielly. To begin with, it embodies two distinct groups 

 of phenomena, which have in reality very little which is essential in 

 common. 



What are usually called ferments are perhaps the most remarkable 

 of all chemical bodies, for they have the power of effecting very i)ro- 

 found changes in the chemical constitution of other substances, although 

 they may be present in very minute quantity; but — and this is their 

 most singular and characteristic property — they themselves remain 

 unchanged in the process. It may be said without hesitation that the 

 whole nutrition of both animals and plants depends on the action of 

 ferments. Organisms are incapable of using solid nutrient matter for 

 the repair aud extension of their tissues; this must first be brought 

 into soluble form before it can be made available, and this change is 

 generally brought about by the action of a ferment. Animal physi- 

 ology has long been ftimiliar with the part played by ferments, and 

 it may be said that no small part of the animal economy is made up 

 of organs required either for the manufacture of ferments or for the 

 exposure of ingested food to their action. It may seem strange at 

 first sight to speak of analogous processes taking place in plants. 

 But it must be remembered that plant nutrition includes two very 

 distinct stages. Certain parts of plants build up, as everyone knows, 

 from external inorganic materials, substances which are available for 

 the construction of new tissues. It might be supposed that these are 

 used up as fast as they are formed. But it is not so ; the life of the 

 plant is not a continuous balance of income and expenditure. On the 

 contrary, besides the general maintenance of its structure, the plant 

 has to provide from time to time for enormous resources to meet such 

 exhausting demands as the renewal of foliage, the production of flow- 

 ers, and the subsequent maturing of fruit. 



In such cases the plant has to draw on accumulated store of solid 

 food which has rapidly to be converted into the soluble form in which 

 alone it is capable of passing through the tissues to the seat of con- 

 sumption. And I do not doubt for my part that in such cases ferments 

 are brought into play of the same kind and in the same way as in the 

 animal economy. Take such a simple case as a potato-tuber. This is a 

 mass of cellular tissue, the cells of which are loaded with starch. We 

 may either dig up the tuber and eat the starch ourselves, or we may 

 leave it in the ground, in which case it will he consumed in providing 

 inaterial for the growth of a potato-plant for next year. But the pro- 



