OF THE SAP OF PLANTS. 



231 



branoh, at the rate of Ifi largo drops porinini;tc, each drop twice 

 or tluice the size of a "minim." ^Neither the catkins nor the leaves 

 of the tree had yet expanded. I at once decided that some interest 

 would attach to a determination hotli of the rate of flow of the fluid 

 and its chemical composition, especially at such a stage of the tree's 

 lite. For although a good deal is already known respecting the 

 *' bleeding " of trees and the general character of the exuding fluid, 

 very much remains to be discovered. Indeed I could scarcely 

 myself hope to do more than confirm some previous observers and 

 perhaps give quantitative value in just one or two directions to the 

 qualitative experiments of others. Thus, that the birch readily 

 yields its sap when the wood is Avouuded is well known. Phillips, 

 quoted by Sowerby, says : 



" Even afflictive birch 

 Cursed by uulettured youth, distils 

 A limpid current from her -wounded bark, 

 Profuse of nursing sap." 



And that birch-sap contains sugar is known, the peasants of many 

 countries, especially Russia, being well acquainted with the art of 

 making birch Avine by fermenting its saccharine juice. 



But after searching two or three large libraries of scientific 

 societies I could not find any hourly or daily record of the amount 

 of sugar-bearing sap which can be drawn from the birch, or that 

 of any sap from any tree, before the tree has acquired its great 

 digesting or rather developing and transpiring apparatus — its leaf- 

 system ; nor could I meet with any extended chemical analysis of 

 sap, either of the brrch or other tree. 



But to proceed with a description of the experiments. A bottle 

 ■was so suspended beneath the wound as to catch the whole of the 

 exuding sap. It caught nearly 5 fluid ounces between eight and 

 nine o'clock p.m. During the succeeding eleven hours of the night 

 44 fluid ounces were collected, an average of 4 ounces per hour. 

 From 8"15 to 9*15 on the morning of the 4th, very nearly 7 ounces 

 were obtained. From 9-15 to lO-lo, with bright sunshine, 8 ounces. 

 From 10-15 until 8.15 in the evening the hourly record kept by 

 my son Harvey showed that the amount during that time had 

 slowly diminished from 8 to a little below 7 ounces per hour. Ap- 

 parently the flow was faster in sunshine than in shade, and by day 

 than by night. The flow was observed from time to time for nearly 

 a week, the rate mentioned being maintained. The wound was 

 ' open altogether for 21 days, hence probably rather more than 17 

 gallons of sap exuded during 20 days of that time; for my 

 excellent gardener, Jonathan White, assured me that the ti-ee had 

 been " bleeding " at about the same rate for fourteen of the fifteen 

 days that elapsed before the matter came under my notice, the first 

 day the branch becoming only somewhat damp. 



it would seem, therefore, that this slender tree, with a stem 

 which at the ground is only 7 inches in diameter, having a height 

 of 39 feet, and before it has any expanded leaves from wdiose 

 united surfaces large amounts of water might evaporate, is able to 



