82 ON SAP. 



vegetable kingdom. The portion absorbed during the 

 night, I suppose, is but inconsiderable. 



Mrs. B. Not so trifling as you seem to imagine ; but, 

 since the whole quantity is restored to the atmosphere 

 during the day, you need not apprehend any dangerous 

 results from its abundance. The Stapadra, the plant 

 which absorbs least, takes in a quantity nearly equal to its 

 own volume during a night ; and the apricot tree, which 

 is at the other extremity of the scale, absorbs eight times 

 its own volume of oxygen gas. 



Succulent plants absorb the least, having the fewest sto- 

 mas; and, after them, plants which grow in marshes ; then 

 evergreens ; and, finally, those plants which shed their 

 leaves in autumn absorb the greatest quantity. 



Emily. It is this, I suppose, which renders it un- 

 wholesome to keep plants in a bed-chamber ? 



Mrs. B. It is ; but, besides this, I should tell you that 

 those parts of plants which are not green, such as the 

 brown stems and branches of a tree, and also the flowers, 

 absorb oxygen both night and day, but in such very mi- 

 nute quantities, as not sensibly to deteriorate the air. 



Let me hear, now, if you can recapitulate the substance 

 of our conversation. 



Emily. The sap rises in plants through two different 

 channels : that which is destined for the nourishment of 

 buds, in shoots of the first year, passes near the pith, and 

 is thence conveyed by appropriate vessels through the 

 wood to the buds ; that which is to feed the plant in gen- 

 eral, rises through the alburnum, and is elaborated in the 

 leaves. 



Mrs. B. Very well ; and in what does this elabora- 

 tion consist, Caroline ? 



Caroline. In preparing the sap to be assimilated to the 

 plant by evaporating great part of the water, and increas- 

 ing the quantity of carbon. The sap contains carbon in 

 two states : first, in that of carbonic acid ; secondly, com- 



' 446. How much oxygen does the stapadra absorb in a night 1 ? 447. 

 How much does the apricot treel 448. What is the order in which 

 different plants absorb oxygen, so far as the quantity is considered^ 

 449. What reason can be deduced from the foregoing remarks to show 

 that plants are unwholesome in a bed-chamberl 450. What further 

 remark in relation to the same subject does Mrs. B. make? 451. 

 By way of recapitulation what account does Emily give of the rising of 

 the sap in plants? 



