INTRODUCTION. 23 



t... 



Caroline. It is doubtless through the vascular system 

 that the sap rises ? 



Mrs. B. The organs of plants are so extremely small, 

 that, though aided by the most powerful microscope, it is 

 frequently difficult to examine the structure of their parts 

 with a sufficient degree of accuracy to be able to ascer- 

 tain their functions. It has long been a disputed point, 

 whether the sap ascended through the vascular or the cel- 

 lular system of organs ; but the latest opinion, and that 

 which Professor De Candolle is inclined to favor, is, that 

 it passes through neither ; and that it rises through inter- 

 stices which separate the different cells. 



Emily. Indeed ! It seems to me very extraordinary 

 that the sap, which performs so essential a part in the 

 economy of vegetation, should not flow freely through 

 appropriate vessels, but be left to find its way as it can 

 between them. 



Mrs. B. The sap, when first pumped up by the roots, 

 consists of little more than water, holding various crude 

 materials in solution ; it is, therefore, more important 

 that the regular organs should be reserved for its elabo- 

 ration, and its conveyance after that process, to the sev- 

 eral parts of the plant. 



The third system of elementary organs is the tracha3 ;* 

 so called from their conveying air both to and from the 

 plant : they are composed of very minute elastic spiral 

 tubes. 



Caroline. But, surely, plants do not breathe, Mrs. B.? 



Mrs. B. Not precisely in the same manner that we 

 do ; but air is so essential an agent, both chemically and 

 mechanically, in promoting their nourishment and growth, 

 that it is scarcely less necessary to their existence than 

 to that of animals. Indeed, it is the opinion of Profess- 

 or De Candolle, that the function of transmitting air is 



* Trachae in anatomy means windpipe. 



65. What does Mrs. B. say has long been a disputed point 1 ? 66. 

 What is professor De Candolle's opinion on the subject'? 67. Of 

 what does the sap at first consist! 68. What is the third system of 

 elementary organs in plants; why do they receive this name; and of 

 what are they composed'? 69. What does Mrs. B. say of air as an 

 essential agent in the production of vegetables'? 70. What does De 

 Candolle suppose in relation to the transmission of air in vegetables! 



