50 



HUTCHINSON'S POPULAR BOTANY 



while in the uninjured tissues, instantly becomes turbid on exposure to the 

 atmosphere. The colour of the latex is usually milk-white ; but yellow, red, 

 and, in rare cases, blue milk-saps are met with. The microscope shows that 

 it consists of a colourless fluid wherein float myriads of minute globules, 

 which give the sap its opaque appearance. The Dandelion (Taraxacum 

 ofiicinale) and Celandine (Ckelidonium majus) are familiar instances of latex- 

 yielding plants. The latter exudes a bright yellow juice if the leaf or stalk 

 be broken. Lettuces, again, when allowed to run up to flower, yield a white 



milky fluid ; and both caout- 

 chouc (indiarubber) and the 

 opium of commerce are simply 

 the dried juices of two world- 

 known plants; caoutchouc being 

 obtained from Hevea brasiliensis, 

 a tall tree of tropical America, 

 and other trees, and opium from 

 the large Opium Poppy (Papaver 

 somniferu'ni). 



The production of caout- 

 chouc by the various species 

 of rubber trees is not so much 

 that man may wear mackin- 

 toshes and tennis shoes, play 

 golf and have rubber tyres to 

 his cycle and motor-car, but 

 that the tree may be protected 

 from boring insects and other 

 afflictions. Mr. Belt makes this 

 clear by telling us* that rubber 

 trees which have been drained 

 of all their milk-sap get into an 

 unhealthy condition, and are 

 soon riddled by boring beetles. 

 If a beetle or a woodpecker 

 begins to bore into a healthy 

 tree, the latex is at once poured 



into the wound, and its poison will drive off the bird, or kill and make 

 a prisoner of the beetle. So freely is this latex poured out to repair any 

 such injury, that it flows in a thin stream down the trunk and, soon 

 coagulating, produces a long, thin, elastic cord, which the natives use 

 for tying up bundles. This, no doubt, first directed man to the valuable 

 nature of indiarubber; and who can properly estimate the importance of 

 that discovery? 



* Naturalist in Nicaragua. 



[. Step. 



FIG. 75. CRUDE RUBBER. 



A- section through a lump of native rubber from the Niger. In this 



condition it contains many impurities, being merely the coagulated 



sap as it has exuded from incisions in the tree. 



