42 PLANT PHYSIOLOGY 



deciding whether they are synthetic or decomposition products of proteid. 

 That the latter are always present in the plant we have already learned ; 

 asparagin has been especially frequently found in plants, and in certain circum- 

 stances accumulates in very considerable amount. It is not one of the bodies 

 arising from the hydrolysis of proteid, yet it is closely related to aspartic acid, 

 which is never absent. The problem is whether the plant, if artificially supplied 

 with amino-acids, amides themselves, or other allied substances, can form proteid 

 from these compounds, and under what conditions that synthesis takes place. 

 Already in older researches on the subject (PFEFFER, Phys. I. 405), nitrates 

 or salts of ammonia were replaced by urea, glycocoll, asparagin, leucin, tyrosin, 

 guanin, creatin, hippuric acid, uric acid, and it was possible to deduce a syn- 

 thesis of proteid from the increase in dry weight that ensued. It is certain, 

 however, that the transformation of these bodies into proteid was not always 

 a direct one, but, for the most part, subsequent to splitting. For example, 

 there can be no doubt that hippuric acid is split into benzoic acid and gly- 

 cocoll, and that the glycocoll only is made further use of. All these substances, 

 however, are readily altered into ammonia by the action of micro-organisms. 

 Although stress has often been laid on the fact that in certain experiments 

 a formation of ammonia could not be proved to occur, it by no means follows 

 that it did not take place. 



It might have been that the ammonia, in such amounts as it occurs, was 

 at once absorbed by the plant. Systematic exclusion of micro-organisms has 

 only recently been effected (BAESSLER, 1887, and especially Luxz, 1899, 1905), 

 and as a consequence there appears to be no doubt that many amino-acids 

 and other nitrogenous organic compounds may serve as a source of N to the 

 green plant. It is by no means the case, however, that, as one would other- 

 wise expect, proteid synthesis is carried on with special ease, for secondary 

 factors, e.g. the feeble permeability of protoplasm to these compounds, often 

 determine whether it shall or shall not take place. More recently, LEFEVRE 

 (1906) has attempted to show that green plants can increase their dry weight 

 in light with the aid of a mixture of amino-acids, even when they are debarred 

 from access to carbon-dioxide ; but in all probability this result is possible 

 only because carbon-dioxide is, in the first instance, split off from the amino- 

 acids in the plant, which afterwards in light proceeds to form carbohydrate 

 from it. Generally speaking, carbohydrates appear to be essential to the 

 formation of proteid from amino-acids ; all the same we must leave it un- 

 decided whether the carbohydrates act as the source of the material or of the 

 energy. According to HANSTEEN (1898) different carbohydrates are essential 

 for the formation of proteid when different sources of nitrogen are employed ; 

 thus with asparagin glucose only, but not cane sugar, is required. Hence one 

 could conclude that this sugar was incorporated into the proteid molecule. 

 The microchemical method employed by HANSTEEN is, however, so uncertain 

 that we cannot attach any value to his results (compare REINHARDT and 

 SUSCHKOFF, 1905). Further, MALINIAK (1900) found proteid synthesis took 

 place in the dark from asparagin just as readily along with glucose as with 

 cane sugar. Her results were, it is true, obtained by quantitative analysis, but 

 all the same they are not quite convincing. Again, we are ignorant what part 

 is played by the light and by the carbohydrate in the working up of amino- 

 acids. In a series of recent researches ZALESKI (1901) and IWANOFF (1901 a), 

 by accurate analytical methods, have shown that proteid synthesis takes place 

 in the dark in resting and sprouting bulbs, tubers, and roots, without any 

 absorption of N from the environment, and without any increase in nitrogen. 

 ZALESKI (1905) has shown the same to be true of seeds . How these proteids arise 

 is not quite certain, but in all probability they are produced from amino-acids. 

 144, 11. 49-51, for at present ... to at all read here ; we may refer, however, 



