ON CAMBIUM. 89 



its liquid form ; in the other it is decomposed, and enters 

 into a chemical combination with v-arious parts of the 

 plant, so as to be identified with its solid tissue, and in 

 such a manner that the dessication will not make it re- 

 appear. 



Emily. But by a chemical analysis would you not 

 discover it ? 



Mrs. B. No ; because it no longer exists in the form 

 of water, but is resolved into its constituent elements, 

 oxygen and hydrogen.* I trust you recollect that water 

 is a combination of these two principles. 



M. de Saussure weighed the water with which he 

 watered a plant ; and after the most careful investigation 

 by mechanical means, both by preserving the water evap- 

 orated, and obtaining that which remained in the plant 

 by dessication, he could not discover above five-sixths of 

 the water he had given to the plant. 



Emily. And is it not known under what form this 

 sixth portion of water exists, in its new combinations in 

 the plant ? 



Mrs. B. The oils and resins with which plants abound 

 contain a very large proportion of hydrogen. There are 

 other vegetable substances which abound with oxygen ; 

 the water, therefore, which so totally disappears, is doubt- 

 less resolved into its two constituents, oxygen and hydro- 

 gen, supplying the oils and resins, and the other juices, 

 with such proportions of these elements as they respec- 

 tively require. 



Carbon is obtained by plants from three different sour- 

 ces : from carbonic acid contained in the sap ; from an- 

 imal and vegetable matter dissolved in that fluid ; and 

 from the atmosphere. 



Caroline. Having so many means of procuring car- 

 bon, no wonder that plants should lay in so large a stock. 



Mrs. B. What part of a plant would you imagine 

 contained the most carbon ? 



* See Conversations on Chemistry, Con. VIII. 



483. What are they* 484. Why cannot that which exists in the 

 second state be discovered 1 ? 485. What experiment was made by 

 Saussure upon the subject"? 486. What question did Emily ask, 

 founded on this experiment! 487. What is the answer of Mrs. B? 

 488. In how many different ways is carbon in plants obtained? 

 8* 



