THE LOCALISATION OF ENZYMES IN PLANTS. 349 



specialised vegetable cell to a complex and well-marked 

 tissue, corresponding closely in structure and function to 

 the secreting gland of the animal body. 



In the simplest cases of secretion we find the ferment 

 formed in the same cell as its appropriate reserve material. 

 Such may be seen in the pollen grains of many plants (11), 

 and in various unicellular fungi. Many pollen grains have 

 been shown to contain either diastase or invertase, or both, 

 and in them simultaneously may be found starch, or cane 

 sugar. In other cases the unicellular organism does not 

 contain such reserve materials, but usually lives in, or upon, 

 a medium which does. The ferment formed by the plant 

 is then excreted into the medium, performs its work there, 

 and the cell absorbs the products of its activity. Such ex- 

 cretion has been shown in the life history of many bacteria, 

 some indeed showing- the power of forming different 

 enzymes according to the medium on which they find 

 themselves (12) growing. In fungi of a little higher type 

 the course of procedure is the same, but the secretion of 

 the enzyme is confined to particular parts of the much 

 branched cell, or to particular, generally terminal, cells of 

 the mycelium. Turning to the higher plants, we find in 

 the pollen tube a similar formation of ferment, which is 

 extruded at definite places, sometimes by well-defined pores 

 into the tissue through which the pollen tube is growing, 

 and which contains the appropriate reserve materials. 



In these comparatively lowly growths, the absence of 

 differentiation renders it extremely difficult to say much 

 about the localisation of the enzyme. Probably it is co- 

 terminous with the cell protoplasm, though more of it may 

 be at one part of the cell than another. In higher plants, with 

 great complexities in the , arrangement of tissues, more 

 approach to specialisation can be seen. 



We find conspicuous cases of very wide distribution 

 even among these higher forms. Thus, diastase has been 

 determined with some precision to exist almost everywhere 

 in the young and green parts of nearly all plants (13), besides 

 being specially marked in parts hidden from the light, such 

 as seeds and tubers. This enzyme varies very much in 



