CHAPTER VI. 

 LATICIFEROUS TUBES. 



Sect. 45. Certain plants, belonging to families or genera to be named below, 

 known as plants which produce milk on injury, contain, in tubes of definite structure 

 and of definite mode of development, a milky opaque fluid, which bears the name of 

 latex ; after this the tubes themselves may be called Laliciferous tubes '. 



The tubes traverse the parts continuously for long distances, adjoining more 

 especially the turgescent, usually parenchymatous elements. They are themselves 

 completely filled with the milky fluid, their walls, though often strongly thickened, 

 are always soft, and easily compressed. Thus if a tube be injured at any point, the 

 pressure exercised by the adjoining turgescent tissues forces the milk out through the 

 opening. 



The wall of the milk-tubes is always a soft, apparently watery cellulose mem- 

 brane, which readily shows the characteristic blue coloration with preparations of 

 iodine. Details of its structure will be given below. 



Within the wall neither protoplasm nor nuclei are to be seen *". It is true many 

 forms of coagulated, finely granular latex, e. g. that of the Cichoraceae, resemble 

 coagulated protoplasm, or there remains here and there, in partially emptied tubes 

 after action of alcohol, solution of iodine, &c., a coat which looks like a coagulated 

 protoplasmic lining to the wall. Further investigations will therefore perhaps be able to 

 prove the presence of a protoplasmic body. Still, as it is difficult to obtain sharp an- 

 atomical evidence of such a body, and as our present knowledge both of the physio- 

 logy and chemistry of latex is scanty, we may regard the contents as being fluids. 



As the name implies, all latex consists primarily of a watery, in itself transparent 

 fluid, in which numerous undissolved small bodies are suspended as an emulsion. 

 In most cases both parts, the fluid and the bodies, are colourless, and the milk white: 

 more rarely the milk is orange-red (Chelidonium), or sulphur-yellow (species of 

 Argemone) ; but it is not possible to define exactly in these cases what share each of 

 the parts takes in the coloration. 



The clear watery fluid contains, as is shown by analyses of those sorts of latex 

 which are used technically, very various bodies in solution ; others, as indicated by the 

 phenomena of coagulation, in a highly swollen state. In these two forms there gene- 

 rally occur in latex, varieties of gum, sugar, small quantities of albumen, often Pectic 



' Milchsaffgefasse, Vasa lactifera, lactea, or Lebenssaftgefasse, Vasa laticis of authors. 

 '' [On this point compare the papers cited below by Treub, Scott, Bower, and Schmidt.] 



