All Gallica |
Books |
Manuscripts |
Maps |
Images |
Periodicals |
Sound recordings |
Scores |
Full record
Titre : Philosophical transactions of the Royal society of London. Series B, Biological sciences
Titre : Philosophical transactions of the Royal society of London. B
Auteur : Royal society (GB)
Éditeur : printed by Harrison and sons (London)
Éditeur : The Royal society (London)
Date d'édition : 1888-1990
Type : texte,publication en série imprimée
Langue : Anglais
Format : application/pdf
Identifiant : ark:/12148/cb34422226r/date
Identifiant : ISSN 00804622
Source : Bibliothèque nationale de France
Relation : http://catalogue.bnf.fr/ark:/12148/cb34422226r
Description : Variante(s) de titre : Philosophical transactions of the Royal society of London
Description : Variante(s) de titre : Philosophical transactions of the Royal society of London
Description : Périodicité : Irrégulier
Description : Etat de collection : 1888 (vol. 178)-1939
Provenance : bnf.fr
Date de mise en ligne : 13/01/2009
1908 (VOL199).
Page
(Screen 416 / 473)
Order a reproduction
To order an image part of a document, please select the desired page, and click "Order a reproduction". In this mode, the images can be requested only one by one. To request a large amount of images or for any other request, please contact us
ce formulaire
Send by e-mail
Search module
Search results
Search this document
Rechercher dans ce périodique
The text below has been produced using a process called optical character recognition (O.C.R.). Since it is an automatic process, it is subject to errors you might find in this page.
The recognition rate for this document is 92,37 %.
DR. A. J. EWART ON THE ASCEXT OF WATER IN TREES. 379
r =
no. la nif^uimNSMti
3 c 2 ̃> -»
vessels for some distance from the eut surface became filled with water, and thèse
columns prevented any backward passage of air. The ibllowiug were the maximal
suctions observed: – Keginning on Mardi 7 at 3.30 p. m., the suction rosé to
-15 centims. (17" C.) at 2 p. m. on thé 8th, fell to – 14"5 centims. by 6 P.M.and
remained at – 14'5 until Mârch 10 at 9 a. m. Thé suction then slowly decreased to
– 7 centims. by March 13 at 9 tlie avernge température having steadily fallen
frorn the 8th to the 13th (17°C. to 3°C.).
During another set of observations' in Àpril the température remained very
constant, averaging 13° to 17° C. during the day time. Started at 2.30 on April A,
the suction rose to –13 centims. by 6 p. m., a/d to –20 centims. by 2 p. m. on thé oth,
remaining at that until 0.30 a. M. of the/next day, and then falling at a rate of'
1| centims. per day until the lOth, wlien/t had fallen to –13 centims. As with the
other manometers, the continuous fa 11 tlie suction of the manometer does not
indicate any corresponding change in the tree, but is in this case due to the gradual
blocking of the vessels nêar to the eut surface cutting off the manometer from
the suction of the functioning wood vessels. Thé gradual entry of air into the
blocked vessels then causes a progressive rise of pressure, and this air may
appear in the vessels so far away from the eut surface that'none is drawn into the
manometer.
Section 14. – Attkmpts TO Demokstkate THE EXISTENCE OF A Pcmping ACTION
IN Transpiring Stems.
Stems of Wifitaria are especially suitable, since long lengths of uniform and
moderate diameter are readily procured bare of leaves, or • with a single leafy
branch only. • They havéj howover^ the disadvantage that the vessels are rather
large, and block rapidly in li/ing wood by gummy ingrowths formed àfter cutting.*
A 4-met're length of a bare stem placed horizontally under a suction of 2 mètres
of water at each end did not pump any water from the vessel attached to the basal
end towards that joiued to the distal one, and air was soon drawn out of the stem.
A similar length of stem was then placed under a head of 68 ceutims.' of- water
at each end.- The water level fell more rapidly in the tube attached to the basal
end, being T2 centims. below that In the tube attached to the distal end in
18 hours, and l'4 below at the end of two days, the total fall being 7 '4* centims.
In a second experiment différences of T4 and T5 were shown at the ends of the
first and second days respectively. On testing these stems, however, under a head
of 1 atmosphère no appréciable flow took place through them, thé terminal mètre of
each being blocked, but the médian 2 metres being open and thé vessels filled with
rarefied air. Hence the difference of level was due to the blocking coupled with the
slightly more rapid absorption at the basal end.
Knowing this, the Japatiese dip the ends of eut flowering stems of IVùtaria in boiling water, which `
keeps them longer fresh and unblocked, but this is inadmissible with experiments on living stems. 'i
Share
Add to your collection
