LIXNEAN SOCIETY OF LONDON. 23 



matter of fact, effect proteolysis, though much less active)}' thau 

 trypsin. If this be established, the result will be that all these 

 proteases will have been found to differ not in kind, but only in 

 degree. They \^-ill form a series in which trypsin, acti^^e alike in 

 peptonisation and in proteolysis, will occupy a central position: 

 on the one hand will be pepsin, with its active peptonisation and 

 slight proteolysis ; and on the other will be erepsin, with its 

 active proteolysis and slight peptonisation. 



It may well be asked, what is the use to plants of the proteases 

 distributed in their tissues ? The importance of these substances 

 to insectivorous plants is sufficiently obvious ; and it is easy to 

 imagine how they may be of service to plants like the Fungi 

 which are parasitic or saprophytic in habit. In both these cases, 

 so far as is known, they serve to supply the plant with organic 

 nitrogenous food from without. But what is the physiological 

 signiticance of these substances in the case of an ordinary plant 

 which does not require to be supplied with organic nitrogen ? 

 The reply to this question is briefly as follows. Normal green 

 plants in their nutritive processes build up, from the simple 

 materials of their food, organic nitrogenous substance which is 

 stored in their tissues in the form of proteid matter that is often 

 insoluble, and in any case is not readily diffusible. Consequently, 

 when these stores of proteid are to be drawn upon for the purpose 

 of growth, it is necessary that there should be some means by 

 which they can be converted into substances which are both 

 soluble and diffusible. This conversion is effected by the proteo- 

 lytic enzymes. Their importance is strikinglj^ illustrated in a 

 germinating seed, where the reserve materials, whether deposited 

 in the cotyledons or in the endosperm, have to be made available 

 for the nutrition of the growing embrj'^o. It is also clear in a 

 germinating bulb or tuber, where the growth of the new shoots is 

 dependent upon the reserves which these organs contain. But it 

 is not limited to such cases as these. It is quite as great under the 

 ordinary circnmstauces of the plant : for it is at all times necessary 

 that the elaborated organic nitrogenous substance should be 

 readily distributed throughout the body. Just as diastase, first 

 discovered in seeds, has been found to occur in all parts of the 

 plant-body where starch has to be converted into sugar, so 

 the proteases are to be found wherever insoluble or indiffusible 

 proteid has to be converted into the soluble and diffusible amidic 

 acids, such as leucin, tyrosin, and asparagin. 



When the digestive activity of certain of the insectivorous 

 plants, such as Xepenthes and Drosera, was first discovered, it was 

 difficult to imagine how these plants should have developed the 

 peculiar faculty of secreting proteases. But in the light of 

 the subsequent discoveries of which I have endeavoui'ed to give 

 you some account, the explanation is simple. If leaves generally, 

 or at any rate commonly produce a protease, it ceases to be 

 remarkable that this should take place in the leaves of insecti- 

 vorous plants. The peculiarity of these plants is now limited to 



