94 Prof. W. Pleffer. The Nature and 



hand, and the operations adapted to the acquisition and absorption 

 of organic nutriment on the other, has led to a grave error, namely, 

 to the assumption that a difference in principle exists between the- 

 metabolism of plants and that of animals. The simple reflection 

 that an immense number of plants exist which are destitute of 

 chlorophyll, might at once have taught that the function of the chloro- 

 phyll apparatus the production of food from carbonic acid and water 

 only serves to provide nutriment for further elaboration, and to 

 introduce it in a peculiar and highly characteristic manner into the 

 organism. For the structural and functional metabolism of green 

 plants, however, the sugar prepared in the plant's own factory has 

 exactly the same significance as the sugar which a fungus obtains 

 from outside. In like manner it makes no difference to the utilisa- 

 tion and importance of sugar in the metabolism of man, whether a 

 sugar-baker obtains it from his own factory or another man has to 

 buy it at second or third hand. 



Again, only those plants can dispense with a supply of albumin- 

 ous food substances which construct these bodies synthetically from 

 simpler compounds. In all plants, however, in close analogy with 

 the animal organism, albuminous substances not only serve as 

 permanent constituents of the body, but are in part again disinte- 

 grated in metabolism. Yet this process does not as a rule result in an 

 excretion of the nitrogenous products of decomposition, for the latter 

 are usually at once re-employed for the regeneration of albuminous 

 substances. This, however, cannot take place to a sufficient extent 

 in cases where a mould fungus is provided with protein substances 

 as its only food, so as to increase the transformation of albuminoids- 

 and at the same time to restrict their regeneration. Under these 

 circumstances a large amount of ammonium carbonate is actually 

 excreted, in oiher words, the same final product which also arises in the- 

 animal body, but which there at once undergoes condensation to form 

 urea. By this latter process the injurious effect which would result 

 from an accumulation of ammonium carbonate is avoided. In the case 

 of fungi such an injurious accumulation does not usually occur under 

 normal conditions of growth, while these plants also to some extent 

 possess the power of guarding against its deleterious influence by 

 neutralisation, owing to the fact that in the presence of alkaline 

 compounds oxalic acid is produced in increased quantity. 



It constantly happens that all those processes which do not 

 form an essential part of the indispensable functional metabolism 

 are regulated in such a manner as to be wholly or partly brought to- 

 a standstill without impairing other functions. Any excessive 

 accumulation of products always has this result, so that, for example, 

 the further formation of sugar or of protein bodies ceases, when 

 these substances have collected in the cell up to a certain limited 



