SECT. II PHYSIOLOGY 227 



Indirectly, of course, chlorophyll and light are of importance in the 

 synthesis of proteids in so far as compounds containing carbon are 

 required, and these are formed in sunlight with the help of chlorophyll. 

 On account of their rich supply of carbohydrates the foliage leaves 

 are specially fitted for the production of proteid, but they are not 

 " organs of proteid formation " in the same degree as they are organs 

 for the formation of carbohydrates. Only in a few plants (nitrate- 

 plants) can the nitric acid be recognised in the leaves ; in most plants 

 it appears to be transformed soon after its alisorption by the root. 



We know as little of the steps in the assimilation of ammonia as 

 of those of nitric acid. Since no preliminary reduction is required, 

 ammonia might be regarded as more readily assimilable than nitric 

 acid ; experiment, however, lends no support to this view. 



The hypothetical intermediate products between the nitrogenous 

 compounds absorbed and the completed proteids, i.e. various amino- 

 acids and related substances, are present in all parts of the plant. 

 Leucin, tyrosin, and asparagin are especially common. It can, 

 however, rarely be determined whether these substances have been 

 synthesised from ammonia or nitric acid or whether they have arisen 

 by the breaking down of albumen. 



While it can be said that the typical autotrophic plant can 

 assimilate nitrogen better as nitric acid than as ammonia, this does 

 not hold for the majority of Fungi. Only a few of these prefer nitric 

 acid ; as a rule ammonia is the best nitrogenous food. Some Fungi 

 lack the power to construct the more complex substances of the plant 

 from such simple nitrogenous compounds, or at least the latter are 

 formed more rapidly and certainly from organic substances. Further, 

 in these Fungi there are various types ; some succeed best with amino- 

 acids, others with peptone, while others prefer proteid. They are all 

 heterotrophic as regards their nitrogenous food. 



The so-called insectivorous or carnivorous plants must be 

 referred to here (^'^). There are plants provided with arrangements for 

 the capture and retention of small animals, especially insects, and for the 

 subsequent solution, digestion, and absorption of the captured animals 

 by means of enzymes. All these insectivorous plants are provided with 

 chlorophyll ; the explanation of their peculiar mode of life can hardly 

 be to obtain organic compounds of carbon. It is further known that 

 they can succeed without animal food, but the modei'ate supply of 

 an animal substance has a distinctly beneficial effect manifested in 

 increased production of fruits and seeds. It is very probable, though 

 by no means established, that the carnivorous habit is a means of 

 obtaining nitrogen. Whether the nitrogen in the peat or Avater in 

 which insectivorous plants often grow is insufficient in quantity, or 

 whether its quality is not optimal must be left undetermined. It is 

 doubtless possible that organically combined nitrogen is specially 

 advantageous to these plants. This does not exclude the possibility 





