THE CONVERSION OF THE PRODUCTS OF ASSIMILATION. II 165 



in barley seedlings, Van Tieghem and Green in pollen-grains ; in a word the 

 wide distribution of invertase can scarcely be called in question. At the same 

 time we do not wish to imply that cane sugar cannot be directly converted in 

 some other way. Still more difficult is the case of maltose. We noted (p. 150) 

 that, according to Beijerinck, dextrose could be formed from starch by means 

 of a special diastase, and this effect might well be produced by the action of 

 glucase, a member of the diastase group. Such a ferment has been shown to 

 occur in yeast, but not much is known as to its occurrence in the higher plants. 

 We must also remember in what has yet to be said that, besides dextrose and 

 levulose, saccharose and maltose may occur as migratory carbohydrates, not to 

 speak of glactose and mannose, about which as yet very little is known. 



Our imperfect acquaintance with the mode of formation of nitrogenous 

 products of assimilation in the foliage leaf has already been frequently noted. 

 Proteids and amides have frequently been found in the leaf ; the amides are 

 capable of translocation without further alteration, but the proteids must, at 

 least in some cases, undergo decomposition first. That such a decomposition 

 of proteid is probable may be deduced from the fact that an accumulation 

 of amides has been observed in such organs as have been kept in the dark 

 (Borodin, 1878). The formation of amides is not influenced by darkening, 

 but the reconstruction of proteid from them is prevented, and hence their 

 accumulation is explained. We have indirect evidence also of the de- 

 composition of proteid. The occurrence of a tryptic ferment in a number of 

 succulent organs has been demonstrated, and this ferment is capable of bringing 

 into solution the proteid formed in the course of assimilation, at all events 

 there is no other purpose known which it could fulfil. The most thoroughly 

 investigated is a trypsin found in the fruit of the pineapple, and which 

 Chittenden (compare Green, 1901, ig8) has termed bromelin. It acts very 

 energetically on fibrin and on egg albumen, and gives as products of its 

 action, peptone, leucin and tyrosin. Were this enzyme limited in its occur- 

 rence to this fruit it would be of little interest to us here, since we are investi- 

 gating the enzymes present in the foliage leaf, but another proteid-dissolving 

 enzyme, papain, known at first only in the fruit of the papaw tree, has been shown 

 by WuRTZ (1879) to occur also in leaves, so that we may believe that bromelin 

 also may occur in the vegetative organs of the pineapple. Tryptic enzymes 

 have also been obtained by Marcano from the expressed sap of the leaves of 

 many species of Agave, by Bouchut and Hansen from the sap of the fig {Ficus 

 carica), and also by Daccomo and Tommasi from Anagallis arvensis (for litera- 

 ture, see Green, 1901, 212 ; compare also Fermi and Buscaglioni). In 

 comparison with the doubtless quite general distribution of diastase, evidence 

 of the occurrence of proteases is as yet very scanty, and it would be rash on 

 our part to conclude from such evidence only that these enzymes were at all 

 generally dispersed. 



Bibliography to Lecture XIII. 



Borodin. 1878. Bot. Ztg. 36, 801. 



Brown and Morris. 1890. Journal Chem. See, Trans. 57, 458. 



Brown and Morris. 1893. Ibid, 63, 604. 



BuTKEWiTSCH. 1900. Ber. d. bot. Gesell. i8, 185 and 358. 



Emmerling. 1901. Ber. d. chem. Gesell. 34, 3810. 



Fermi and Buscaglioni. 1899. Centrbl. Bakt. II, 5, 63. 



Fleissig. 1900. Physiol. Bedeutg. d. olartigen Einschl. in Vaucheria. Diss. Basel. 



Frank. 1866. Jahrb. f. wiss. Bot. 5, 161. 



GoDLEWSKi. 1877. Flora, 60, 215. 



Green. 1887. Phil. Trans. 178 B, 39. 



Green. 1890. Proc. Roy. See. 48, 370. 



Green. 1897. Phil. Trans. 188 B, 167. 



