Significance of Functional Metabolism in the Plant. 95 



amount. On the other hand, the inevitable final products of the 

 general functional metabolism must be continually formed, for it is 

 upon this chemical process that the maintenance of vital activity 

 depends, and these final products, in so far as they are not again 

 made use of, must also be constantly secreted and removed, for their 

 accumulation would render further activity impossible. In many 

 aerobic organisms, for reasons already indicated, only the excretion 

 of carbonic acid and water is in question. In the case of many fungi, 

 and some other plants, we find, however, in addition to these sab- 

 stances, organic acids, and other non- volatile final products, which are 

 secreted in great variety and amount, especially in the case of many 

 aerobic and anaerobic fermentations. 



In order to avoid an accumulation in the cell, the final products 

 which are continually arising, as well as the food to be assimilated, 

 must necessarily be soluble and capable of diosmosis. Hence the 

 ejection of the undigested remains of food is usually impossible, 

 though, where it is possible, we find it in plants as well as in 

 animals, as, for example, in the Myxomycetes. Extracellular diges- 

 tion, which is employed on an extensive scale even in the vegetable 

 kingdom, is, broadly speaking, only a means by which substances 

 are rendered available for absorption and elaboration by the 

 living elements, but is no more an integral part of the actual func- 

 tional metabolism than is the digestion in the stomach of animals. 

 The same holds good with reference to respiratory movements, and to 

 all those operations and adaptations which provide for the access of 

 oxygen and the removal of carbonic acid. In plants, it is true, there 

 are no special active respiratory movements, but in all the larger plants 

 an extensive system of aeration serves to maintain, adequately, 

 the gaseous interchange of the internal cells. A loose combination 

 of oxygen, such as is found in the haemoglobin of the blood, is not 

 of general occurrence among plants, though present and efficient in 

 certain chromogenic bacteria. 



If we leave out of consideration all subsidiary and preliminary 

 processes, there is no doubt that the true aerobic functional meta- 

 bolism is the same, in principle, in plants and in animals ; in fact 

 even from a formal point of view, no difference exists, if, as is fitting, 

 we select the lowest animal and vegetable beings for comparison. 



In plants, which like animals perform a large amount of work, 

 vigorous respiration also takes place ; in specially active plants it 

 may even be actually greater than in warm-blooded animals. For 

 while in man, the carbonic acid produced in twenty-four hours amounts, 

 to about 1*2 per cent., in many mould-fungi it exceeds 6 per cent, of 

 the weight of the body ; in very active bacteria the consumption of 

 oxygen, referred to the same standard, may reach an amount 20(X 

 times as great as in man. 



VOL. LXIII I 



