258 BOTANY PARTI 



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 (cf. p. 266). 



Nitrogen is present not only in proteids but in LECITHINS and in 

 ORGANIC BASES. The former are complex esters in which glycerine is 

 combined with two molecules of fatty acid, one molecule of phosphoric 

 acid, and the nitrogen -containing base, cholin. They are never 

 absent from living protoplasm. The majority of organic bases 

 (alkaloids) are probably by-products of the assimilation of nitrogen 

 and are not further utilised. 



While it can be said that the typical autotrophic plant can 

 assimilate nitrogen as well or 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 sub- 

 stances. 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 nitro- 

 genous food. 



The so-called INSECTIVOROUS or CARNIVOROUS PLANTS must be 

 referred to here ( 35 ) (cf. p. 185). These are plants provided with 

 arrangements for the capture and retention of small animals, especially 

 insects, arid 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 moderate 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 water 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 that the insectivorous habit is related not only 

 to the supply of nitrogen, but to that of other nutrient salts, especially 

 of potassium and phosphoric acid. Whether these salts are utilised 

 in organic combinations or are transformed in the digestive process to 

 the inorganic form is unknown. In the latter case the use of the 



