FORMATION OF PROTEIDS. 335 



portion as their cells divide. Whether this occurs simultaneously with assimila- 

 tion in the light, or subsequently during the following night, is of course not 

 known. At any rate, the facts brought forward teach that proteid-like compounds 

 from which protoplasm arises can be formed independently of assimilation, provided 

 only that the necessary constituents are conveyed to the cells concerned. Among 

 these constituents an organic carbon compound is essential ; and this, in its turn, is 

 of course to be finally derived — though it may be by the most various and round- 

 about ways — from the starch assimilated in the chlorophyll. 



In the case of highly organised plants I have already sought to render it pro- 

 bable that the formation of proteid substances takes place in the sieve-tubes of the 

 vascular bundles. The sieve-tubes in the younger shoot-axes and leaves contain an 

 amorphous proteinaceous slime, which is by no means to be confounded with pro- 

 toplasm. It consists, to use a modern expression, not of organised or living, but 

 of circulating proteids, evidently being conveyed through the sieve-tubes to the younger 

 growing organs. We have many indications, however, that it is probably also formed 

 in these sieve-tubes : in the first place we find in the neighbourhood of the sieve- 

 tubes of the organs in question, regular layers of cells which contain fine-grained 

 transitory starch and sugar, and extremely fine-grained starch is frequently found in the 

 slime of the sieve-tubes themselves. I regard this starch as one of the constituents 

 from which the proteinaceous slime of the sieve-tubes is to be formed. Holzner 

 long ago gave expression to the idea that the formation of oxalic acid in the plant 

 is for the purpose of decomposing the calcium sulphate taken up by the roots, 

 and thus setting free the sulphuric acid for the formation of proteid substances 

 which contain sulphur; and it is certainly an observation favourable to this sup- 

 position that, very generally, layers of cells in which calcium oxalate crystallises out 

 run in the neighbourhood of the bundles of sieve-tubes, from which indeed it may 

 well be concluded that the sulphuric acid in the calcium salt may be employed 

 here or in the neighbourhood, or even in the sieve-tubes themselves, for the 

 formation of proteid substances. With respect to the third ingredient, a salt of 

 nitric acid, we know that saltpetre is distributed in the tissues of a normal plant.. 

 The constituents are thus given, and the result, the proteinaceous slime in the sieve- 

 tubes also. The reply to these suggestions, that the quantity of calcium oxalate 

 does not accord with the amount of sulphur contained in the proteid substances in 

 question, appears to me of little weight, since, on the one hand, a decomposition of 

 calcium sulphate by means of oxalic acid may take place also for other purposes 

 in the plant, and thus under certain circumstances (e. g. in some species of Cactus 

 and Aroideae) an enormous quantity of calcium oxalate be accumulated, while in 

 other cases, on the other hand, the decomposition of salts of sulphuric acid may 

 occur without the formation of calcium oxalate. 



However, the formation of proteid substances in the plant may also take 

 place in another way, and perhaps in any parenchyma cell whatever, since it may 

 be that another body abounding in nitrogen, one of the group of amides, is first pro- 

 duced, namely, asparagin, a crystallisable substance soluble in the cell-sap, but which 

 contains no sulphur. Asparagin, as recent researches, especially those of Borodin ^ 



' Borodin, Bot. Zeitwng, 1878, p. 801, 'Ueber die VerbrHlung des Asparagins^ 



