5 82 



TRANSLOCATION 



occur in abundance in certain varieties of latex '. These substances do not seem 

 to be merely unavoidable by-products, but appear to have a certain economic 

 value, for certain constituents of latex give it the power of coagulating when 

 exposed to air, and hence enable it to protect a wounded or exposed surface. 

 Similarly its poisonous properties act as a protection against insects or herbivorous 

 animal 2 , and it is possible that herein lies the importance of the latex and lactiferous 

 tubes in many plants, although in other cases the latex system may serve to 

 a certain, or even to a marked extent for the conveyance of plastic materials. 



In certain cases at least the plastic substances diminish at certain stages of 

 development, or during starvation, as Schullerus 3 found to be the case with the 

 starch in the latex of Euphorbia, and sugar in that of Moms. A certain amount 

 of the emulsified substances may also be re-assimilated, for Faivre found the latex 

 in seedlings of Tragopogon porrifolius became clearer in darkness, or in an 

 atmosphere free from carbon dioxide, but quite milky again when photo-synthetic 

 assimilation was allowed to recommence. Faivre also concluded on similar grounds 

 that the latex of Morus alba has a nutritive value and contains a large amount of 

 stored food during winter, and his ringing experiments on various species of Fiats 

 seem to indicate that the latex system is of marked importance for the transference 

 of nutrient and plastic substances 4 . The milkiness of the latex is a very unsafe 

 index to employ, and Hanstein 8 has in part obtained contradictory results to Faivre. 

 The structure and arrangement of the lactiferous tubes renders them markedly 

 adapted for translocation, and various causes may induce streaming currents of 

 latex to move from one part to another in intact plants". These characteristics 

 are, however, of similar importance for the conveyance of latex to a wound, and the 

 anatomical arrangements are equally adapted for the performance of the protective 

 and biological functions already mentioned, so that a definite decision as to the 

 functional value of the latex system is not at present possible (cf. Schimper, Bot. 

 Zeitung, 1885, p. 771). 



Historical. Malpighi's conclusions as to the circulation of food-materials in 

 the plant were altogether remarkable considering the epoch at which they were 

 made, but as the result therefrom a one-sided and incomplete theory of sap 



1 For analyses of latex, cf. de Bary, 1. c., p. 194 ; \Viesner, Die Rohstoffe d. Pflanzenreiches, 

 1873; Boussingault, Agron., &c., 1894, T. vir, p. 64 (Cow-tree) ; Chimani, Bot. Centralbl., 1895, 

 Bd. LXI, p. 385. Microchemical methods, Schimper, Flora, 1890, p. 228. 



' De Vries, Landw. Jahrb., 1881, p. 687; Ludwig, Biol. d. Pfl., 1895, p. 231; Zander, Bibl. 

 Bot., 1896, Heft 37, p. 37; B. H. Biffen, Annals of Botany, 1897, Vol. xi, p. 334. The importance 

 of the peptic enzymes occurring in certain forms of latex is not yet certain. 



3 Schullerus, Die phys. Bedeut. d. Milchsaftes v. Euphorbia, 1882, p. 92 (Sep.-abdr. a. d. Abh. 

 d. Bot. Vereins Brandenburg, Bd. xxiv) ; Treub, Ann. d. Jard. bot. d. Buitenzorg, 1882, T. in, p. 37. 

 Cf. Schimper, Bot. Zeitung, 1885, p. 774. 



4 Faivre, Compt. rend., 1879, T. LXXXVIII, p. 369 ; Ann. d. sci. nat., 1866, v. se"r., T. VI, p. 33 ; 

 1869, T. x, p. 97. 



5 Hanstein, Die Milchsaftgefasse, 1864, p. 54. On aggregations in latex, cf. Schwendener, 

 Monatsb. d. Berl. Akad., 1885, p. 335. 



8 Cf. Schwendener, 1. c., p. 326. Usually no latex escapes from withered plants or from the 

 older parts when cat. 



