THE LOCALISATION OF ENZYMES IN PLANTS. 343 



decomposition, or splitting- up of the very complex substances 

 into more simple ones, capable of travelling from the centre 

 of deposition and of immediate assimilation. We have, 

 indeed, the process typically shown in the animal body, a 

 true digestive act. Moreover, in plants as well as animals 

 this digestion is carried out by the agency of enzymes or fer- 

 ments. These bodies, indeed, with the doubtful exceptions 

 afforded by the so-called carnivorous plants, seem to be 

 formed entirely with a view to the utilisation of the reserve 

 materials, deposited as we have seen in the plant tissues, 

 when constructive metabolism is in excess of immediate 

 requirements. 



In seeking to determine the distribution of ferments or 

 enzymes in the plant tissues it is advisable first to ascertain 

 where the reserve materials are deposited, and in what 

 forms. In many cases this is extremely easy. Seeds, 

 tubers, bulbs, fleshy stems and roots may be seen to contain 

 them in large quantity. The cells are frequently found to 

 be crowded with starch grains, drops of oil, or proteid 

 materials, in the form of aleurone grains ; the cell-sap may 

 be found to contain large quantities of soluble carbohydrates, 

 such as sugar or inuline. In certain cells in the wood of trees 

 the winter supply may be demonstrated to exist in various 

 forms, of which starch is the most widely distributed. In 

 other cases the detection is more difficult ; complex gluco- 

 sides are found by proper treatment to be present in more 

 restricted localities. Compounds of phosphorus may be 

 detected stored up in definite layers of cells in particular 

 seeds ( 1 ). All these forms are intended to nourish the 

 plant during seasons of inactivity lasting for some time. 

 From certain recent researches (2), it appears that the 

 starch grains that are so constantly seen in the chlorophyll 

 corpuscles of the leaves during vigorous assimilation, are 

 equally reserve materials, intended primarily to nourish the 

 plant during the period of darkness, or to be transported 

 later to more permanent reservoirs. In the very simplest 

 plant, whose body is composed of only a single cell, these 

 materials may be found to be stored up in the protoplasmic 

 contents, and to disappear at particular times. 



