METABOLIC PROCESSES IN THE PLANT. 359 



1 See Sachs, Botan. Zeitung, 1862. 



2 See Wilhelm, Beitrage zur Kenntniss des Siebrl>hrenapparates dicotyler. 

 Pflanzen, Leipzig, 1880, and Fischer, Untersuchiuijeii iiber das Siebrohren 

 system dcr Cucnrbitaceen, Berlin, 1884. 



144. Latex. 



Many plants,'as is known, contain latex. If we cut a Euphorbia, 

 for example, a white milky juice often escapes from the wound in 

 large quantities (especially if we experiment with the Cactus-like 

 Euphorbias). 



Clearly the contents of the latex reservoirs must stand at a 

 not inconsiderable pressure, exerted by the turgescent cells of the 

 parenchyma in their neighbourhood, because otherwise such large 

 quantities of fluid could not flow from the wound as is actually 

 the case when laticiferous plants are cut. 



The question as to the physiological function of latices is still 

 unsolved. I cannot escape the impression that latices are inter 

 alia of significance in nutrition ; the experiments of Faivres are 

 also in favour of this. Latex may, however, be of special im- 

 portance as a means of protection to the plants. 



In the watery fluid of latices, as in the serum of the milk of 

 animals, there are suspended numerous small solid particles, so 

 that most latices appear white in colour. The number of these 

 solid particles, however, varies considerably from time to time, 

 and according to the origin of the latex. If we take a drop of 

 latex from the stems or the leaves of a fig, and mount it on a 

 slide without addition of water, we can easily make out by 

 examination under high magnification that the number of 

 particles in suspension is comparatively small. The latex of 

 the Euphorbias, and that of Ficus elastica are usually found 

 to be much richer in solid constituents. 



In the watery fluid of latices there occur in solution mineral 

 substances, sugar, proteids, and sometimes also pepsin (see 96), 

 etc. The suspended particles very often consist mainly of 

 indiarubber. Many latices, however, also contain fat or starch 

 grains. 



If latex from a Euphorbia is mixed on the slide with a little 

 water or alcohol, the latex coagulates. Under the microscope 

 it is seen that the constituents which were originally uniformly 

 distributed in the latex have gathered themselves together into 

 larger masses. 



