1916] CURRENT LITERATURE 327 
wall, but the wall is deformed with the protoplast, owing to the cohesion of 
the contained water. Very considerable negative pressures or tensions of water 
can thus be developed in plant cells before bubble formation occurs; 250 
cells of orchids and the pith of orchid and Sambucus stems. This is independent 
of living protoplasm, for it occurs in dead cells. In thin-walled parenchyma the 
cells may be completely crushed without gas appearing, while in thick-walled 
tracheae are still free fron gas, which means that the water within them must 
be under negative pressure equal to the osmotic pressure of the parenchyma. 
Vessels in storage organs withstand little negative pressure, while those of 
actively conducting tissue develop great negative pressure without bubble 
formation within them. If in wilted tissue air is admitted to a vessel by a 
wound, it does not pass through the side walls to intact vessels, although they 
bear water under considerable tension. When both sides of the cell wall are 
water free, air accumulates within rapidly even under slight negative pressure; 
while the cell is full of water, air does not accumulate negative pressure 
within even under many atmospheres. 
In another article UrsPRUNG’ raises the question of the cause of bubble 
formation in ‘“Tonometern,” any apparatus used for the qualitative or quanti- 
tative determination of fluid cohesion. For water he believes bubble formation 
is not determined by the limits of cohesion, for the cohesion of water as meas- 
ured by such instruments falls far below the cohesion calculated by VAN DER 
WAALS on the theoretical basis. The great variation in the tension at which 
bubbles appear, even under like conditions, also argues against the limits of 
cohesion being the cause of bubble formation. Since all evidence indicates 
that adhesion of water to the wall exceeds its cohesion, URSPRUNG believes 
that the limits of adhesion do not determine bubble formation. GERNEZ 
surfaces bear adsorbed gas as inoculation centers. UrsPruNc believes that 
adsorbed gases (in very thin layers of submicronic or amicronic thickness) on 
_ the walls of the “Tonometern” cause bubble formation. Hence all attempted 
upon cohesion within tracheae, URSPRUNG emphasizes the fact that wood tissue 
adsorbs gas readily. The author uses considerable space in criticizing Drxon’s 
experiments ——— cohesion of water 
7 Urspruna, A,, ister die Blasenbildung in Tonometern. Ber. Deutsch. Bot. 
Gesells. 33:140-153. 1915. 
