I'i'.KIOUK .\l, l,n I'.KA'I I'KI', Hi 



tlic s:ip I'l'Mii the siij^'.'ir in.iplf \vli< ii l.-q^ijiwl is greater diiriii^' llic night. 

 It Hows fifjiii the upper f<l(^c of the woiiii'l, showiiif^ that it does not 

 come from the roots hul from the lo|)." The transfer of S(;h,',>I • salts 

 from the loots to the leaves is assuinerl to laUe place hy simple diffiiHon 

 through the moisture contaiiierl in the cell walls. 



Ill regard to ihe drying of liniher .Mr. Stone suggests a refrigerating 

 condensing process, thus supplying dry, cool air to the vvoofi. In jjrac 

 lice such a prfjcess uriuld not produce good drying nor he ecrMiomical. 

 While his idea of the exi»lanatifjn oi the physical phenfjiiienon of 

 transfusif;!) of I he moisture thrfMigh the stick oi woorl is g(;orl, his 

 assimijition that the same principle holds goorl for firying wfxid in 

 the air, is wrong on account of many other factf^rs which cf»nie in to 

 modify the action. 



The hypothesis of the ascent (jf sap seems so well taken aiul well 

 supporter! hy facts that I might venture to add a few cfjiiiments of my 

 (Avn to this review. Several years ago I had shf^A'U ex|)erimentally 

 that moisture transfuses through wofid from the hot toward the colder 

 surface, and I explained this action on the theory of successive evap- 

 oration and rccftndensatirjii within llic cell hiniina. In the absence of 

 air a very slight difference in temjjerature will cause this action to 

 jjroceed rajjidly ; in fact, as fast as the transference oi heat can take 

 place. The [presence of air would greatly retard it. In th(; living tree, 

 there is |;rohahly little air in the vessels of the sapwoofl rluring rapid 

 growth. The hypf>thesis seems so plausihle that it might inrleed, be 

 carried a step further, anrl the function of the jAculiar valve-like 

 JKjrdered pits f^f the traclieid^, a long time hidden prr»hlem, he accfjunterl 

 fot. Suppose that tlu,- membranes of these marvelous structures allow 

 the water-vapor to pass freely through when the tf/ri are centrally 

 locaterl (which is certainly the case;. If the teniperalure of a series 

 of tracheids be now sufficiently cooler at nighi than contiguous ones 

 l)elow, as to cause them to become filled with water through coiulensa- 

 tion, the pressure of this water column might become sufficient lo 

 elfjsc the valves of the bordered pits and thus j)revent the water from 

 escajjing riownward when the temperature changes, as in the fol!owin</ 

 day time for instance, 'j'hus a means woubl be ]>rf)videfl for accumu 

 lating water, thrfjugh small changes in temperature, passing ui)ward bv 

 vaporization and being preventerl from flowing downwarrl by its own 

 weight anrl the valve action of the bfjrdered pits. 



II. h. Tir.Mxsv. 



