382 University of California Publications in Botany [VOL. 5 



/. POSSIBLE AGENCY ACTIVE IN THE DISSOLUTION OF 

 THE MIDDLE LAMELLA 



The pectose of the middle lamella may be broken down into the 

 soluble pectin in three different ways by the action of an acid, 

 of an alkali, or of the enzyme pectosinase. Since it is doubtful 

 whether alkaline reactions in living cells frequently get strong enough 

 to affect the middle lamella, the probable active agency is limited 

 to the acid or the enzyme action. Up to the last few years very 

 little has been known about the action of enzymes concerned in 

 pectic digestion. It has been natural, therefore, for investigators 

 (cf. Wiesner, 1905, and Kubart, 1906) to consider the acid as prob- 

 ably the active agency. In this connection, it is well to state that I 

 have obtained distinct acid reactions with litmus from the base of the 

 corolla of Nicotiana during abscission. This would confirm Kubart, 

 who, it will be remembered, obtained similar reactions from the corolla 

 of Nicotiana. But in this case I sometimes obtained acid reactions 

 from the corolla when in the normal condition. Since these observa- 

 tions offer no detailed evidence that acidity has increased during 

 abscission to a degree higher than normal, their significance can well 

 be doubted. 



The tissues of Datura give a distinct acid reaction to litmus in the 

 normal condition. Experiment 3 below shows a slight increase in 

 acidity during abscission. No acid reactions of much intensity are 

 given by the base of the pedicel of Nicotiana either in the normal or 

 abscissed condition. 



Experiment 3. Lot A contained the bases of three pedicels cut 

 while abscission was going on. Lot B contained an equal weight 

 (6 gin.) of the bases of three pedicels cut in the normal condition. 

 These were extracted with water and the extracts made up to 10 cc. 

 each. By titration with 10 per cent NaOH and phenolphtalein the 

 following results were obtained : 



A 0.75 cc. required to neutralize 



B 0.6 cc. required to neutralize 



A similar experiment on Nicotiana showed, however, that the nor- 

 mally low acidity of this genus is slightly reduced during abscission, 

 as indicated by the following results: 



A 0.25 cc. required to neutralize 



B 0.37 cc. required to neutralize 



