CIRCULATION OF SAP. 9? 



have various Junctions ; they permit of the 

 evaporation of superfluous moisture and gases, as well 

 as the absorption of the same from the air, -as conditions 

 a^c changed. So long as the leaves are supplied with an 

 abundance of .moisture through the roots and stems they 

 wall take none from the air, but let the supply be cut off 

 from below and have it presented to the leaves, and a 

 reverse action coon follows. We may test this reverse 

 movement very readily with leaves and twigs cut from 

 growing plants, and at the same time it may be seen that 

 the absorption of moisture varies under different circum- 

 stances and conditions. l!]ie force exercised by the roots 

 is by far the greatest ; next in degree is the absorption of 

 liquids by the exposed cells in the severed stem, and last 

 and least through thejoores or stomata of the leaves. Of 

 the many experiments I have made in investigating the 

 movements of liquids in plants, I may refer to one which 

 has a direct bearing on this question of absprption of 

 moisture through the stomata of the leaves. V I cut off 

 small, tender branches and leaves of various plants, such 

 asAchyranthus, Coleus, Verbenas, Abutilons, etc., spread 

 them all out on a shelf in the sun, where they soon began 

 to flag, and after all had become fully wilted, the severed 

 ends of one-half of each variety and kind were dipped in 

 melted wax in order to hermetically seal up the exposed 

 cells. Then all were placed in a box and lightly sprinkled 

 with pure water. At the end of twelve hours they were 

 taken out and carefully examined, and the difference in 

 the condition of the sealed and unsealed was quite ap- 

 parent ; those with exposed severed cells had fully revived, 

 while many of the others were still limp, but all showed 

 signs of recovery. The cuttings were all replaced in trie" "box 

 and left there another twelve hours ; then all were found 

 to have recovered and to be as fresh as when first taken 

 from the parent plants. This experiment shows that 

 absorption of moisture may take place through the 



