378 University of California Publications in Botany [Vol. 5 



c. EXPERIMENTAL EVIDENCE FOR THE DISSOLUTION OF 

 THE MIDDLE LAMELLA 



It is supposed that the middle lamella, or primary cell membrane, 

 is largely composed of calciiun pectate, a calcium salt of pectic acid 

 which has been given the general name pectose. The secondary cell 

 membranes probably contain a larger proportion of cellulose with 

 the pectose than is present in the primary membranes. This pectose, 

 which is of course insoluble in water, is disorganized by a process of 

 hydrolysis to form pectin. The pectin, which is a colorless mucilagi- 

 nous substance, is readily soluble in water but is precipitated along 

 with the proteids and enzymes of the protoplast by the addition of 

 alcohol. Thus, if a water extract is made from separation zones dur- 

 ing the first stages of abscission, one would expect to get a solution of 

 several substances, among which would be the pectin produced by the 

 dissolution of the pectose in the primary cell membranes. It might 

 be expected that the amount of precipitate obtained from this extract 

 with alcohol would be greater, provided the amount of other sub- 

 stances remained the same, than the amount of precipitate obtained 

 in a similar manner from separation zones in which there had been 

 no abscission and in which no pectin had been formed. Whether or 

 not the increase in the amount of precipitate is due to the added 

 pectin cannot of course be proven without actual chemical analysis, 

 and such an analysis would be difficult because of the very small sam- 

 ples of material obtainable. However this may be, any difference in 

 the amount of precipitate would be of interest. 



This experiment and the two which follow are, as far as I have 

 been able to determine, the first of their kind. Apart from this fact, 

 their chief value probably lies in the fact that they suggest a line of 

 investigation which, if carried on in more detail and with better 

 facilities, will undoubtedly lead to important conclusions. These 

 experiments were, however, carried on with as much care as possible 

 and since the results of duplicate tests are in agreement, they give, as 

 far as they go, dependable results. 



After several experiments indicating the results given below, the 

 following test experiment was performed: 



Experiment 1. — Two water extracts of equal concentration were 

 made from the lots of material. Lot A contained 200 small pieces of 

 the pedicel in which the separation zone was located and in which 

 abscission had started. Lot B contained an equal weight of a similar 



