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be formed by the decomposition of carbonic acid 

 amongst water, with whose elements the young carbon 

 combines. The first secretion that we find in a young 

 seedling is gum, and out of that gum the organs of 

 the tender plant are fashioned by the vital force. 

 The first secretion that is formed by a full-grown 

 plant, when it is roused from its winter's torpor and 

 begins to grow, is gum, which in trees oozes out be- 

 tween the wood and bark, as cambium, causing the 

 latter to "run," and enabling both those parts to 

 increase in thickness. Gum also lubricates the delicate 

 organs which are formed in the leaf-bud, and lengthen 

 into leaves and branches. But as plants grow old gum 

 disappears, the proportions of its element change, and 

 it assumes the new forms of starch and wood, or it 

 simply loses the water that dissolved it, and becomes a 

 hardened coating to the minute cells and tubes of vege- 

 table structure. When it is completely changed, or 

 hardened, wood is said to be ripe ; on the contrary, when 

 it remains in the very state of gum, and still retains its 

 water, wood is called unripe. In the former condition 

 it offers great resistance to changes of temperature, suf- 

 fering but little either from heat or cold, and it gives 

 birth to branches firm and healthy like itself, because 

 they are fed by a healthy mother. In the latter 

 state, (that of unripeness,) it is extremely sensible of 

 changes of temperature, its fluid expanding with force 

 on either side of 40 degs. of Fahrenheit's scale, and 



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