VEGETABLE PROTEIDS. 51 



Vegetable proteids. The amount of proteid matter in plants, 

 especially in those which are full grown, is less than in animals. It occurs 

 dissolved in their juices, or in their protoplasm, or deposited in the form 

 of granules called aleuron grains. Plant proteids have frequently been 

 obtained in a crystalline form. They may be divided into the same 

 classes as the animal proteids. 



Class 1. Albumins. Small quantities of true albumin have been 

 described by S. Martin x in the juice of the papaw fruit, and by Green 2 

 in the latex of several caoutchouc-yielding plants of the natural orders 

 Apocynese and Sapotacese. 



Class 2. Globulins. These are by far the most abundant natural 

 proteids present in plants. This view, which was taken by Hoppe- 

 Seyler, 3 is contrary to that of Kitthausen, 4 who regarded vegetable 

 proteids as consisting chiefly of legumin and allied substances. 5 



Class 3. Albuminatcs. Acid and alkali albumin are formed readily 

 from vegetable proteids, especially from plant myosin. Legumin or 

 vegetable casein was used synonymously with vegetable proteid by some 

 of the earlier investigators, 6 but it is now usually regarded as alkali 

 albumin, formed artificially in the extraction of the globulins by alkali. 

 The name conglutin was introduced by Kitthausen 7 for the more 

 glutinous product obtained from almonds and lupins. 



Class 4. Proteases and peptones. Proteoses have been described in 

 latex, in papaw juice, and flours of different kinds. True peptones are 

 not found in the circulating juices of plants. Probably the circulating 

 proteids in plant life are proteoses, hemialbumoses (Vines), though amido- 

 acids (leucine, tyrosine, asparagine, adenine, etc.) 8 also occur. These 

 substances are formed by proteolytic ferments during germination. The 

 best known of these ferments, papain, has been investigated by Wurtz, 

 Martin, and others. Such ferments, as well as malting ferments, which 

 convert the insoluble starch of the seed into the soluble sugar, are probably 

 almost ubiquitous. 9 In carnivorous plants, another ferment is met with 

 of a somewhat different character. 



Class 5. Coagulated protvids. Vegetable albumin and globulin, like 

 those of animal origin, are converted at a high temperature into an 

 insoluble heat coagulum. 



With regard to the value of vegetable proteids as food, it may be stated that 

 as a rule they are not nearly so readily digested as animal proteids. Prausnitz 10 



1 Journ. PhysioL, Cambridge and London, vol. vi. p. 336. 



- Proc. Roy. Soc. London, vol. xl. p. 28. 

 3 "Physiol Chem.," S. 75. 



* Ztschr. f. Chem., Leipzig, Ser. 2, Bd. iv. S, 528, 541; vi. 126; Journ. f. praJct. Chem., 

 Leipzig, Bd. ciii. S. 65, 78, ]93, 273. 



5 Ritthansen defends his view in Chem. Centr.-BL, Leipzig, 1877, S. 567, 578. 



6 Einhof, Neue allg. Journ. d. Chem., v. A. Gehlen, 1805, Bd. vi. S. 126, 548. Dumas 

 and Caliours, Liebig, and others also examined this substance. 



7 Ibid., Ser. 2, Bd. xxvi. S. 440. 



8 E. Schulze and E. Kisser, Landw. Versuchs Stat., Berlin, Bd. xxxvi. S. 1 ; E. Schulze, 

 numerous papers in Ztschr. f. physiol. Chem., Strassburg. See especially Bd. xii. S. 405. 



9 Gorup-Besanez, Ber. d. deutsch. chem. Gescllsch., Berlin, 1874, S. 1478 ; Krauch, 

 Journ. Chem. Soc., London, 1878, Abst. p. 996 ; Green, Proc. Roy. Soc. London, vol. 

 xli. p. 466; Thiselton Dyer's Presidential Address, Sect. D, Brit. Assoc., 1888; Hansen, 

 Bot. Ztg., 1886, S. 137; Ellenberger and Hofmeister, CentralU. f. auric. Chem., Leipzig, 

 1888, S. 319. The subject of enzymes and reserve materials in plants, however, is now 

 a very large one, and it will be found discussed, with bibliography, in a series of articles by 

 J. Reynolds Green, in Science Progress, London, vol. i. p. 342 ; ii. p. 109 ; iii. pp. 68, 376 ; 

 v. p. 60. 



10 Ztschr. f. BioL, Miinchen, Bd. xxiv. S. 227. 



