6 BOTANICAL GAZETTE [JULY 
makes possible the splitting of the membrane, the formation of 
intercellular spaces, and an exudation of material to form the 
knobs, points, and other structures already referred to. 
A further proof of the presence of pectic compounds in the wall 
is furnished by treating tissues with a cellulose solvent; the gen- 
eral outlines of the cells remain, the middle lamella, and often a 
large part, or in some cases all, of the other wall layers preserving 
their form. The framework thus left takes up pectic acid stains. 
and is indifferent to cellulose stains. The best distinctive stain 
for pectic substances is ruthenium red, the ammoniacal sesqui- 
chlorid of ruthenium. Our knowledge of the value of this sub- 
tance is due to Mangin (8), who first described its remarkable 
properties as a staining reagent for vegetable tissues. 
Mangin’s attention, it is seen, has been directed to the 
chemical composition and transformations of the “ intercellular 
substance,” and he has not connected his valuable results 
obtained in that field with a study of its origin. It was in part 
to supplement his work in this important regard that the present 
investigation was undertaken. 
Strasburger (12) and Dippel (2) accept Mangin’s conclusions 
as to the widespread presence and the importance of pectic sub- 
stances in plant tissues, especially in the middle lamella and the 
thin layer immediately surrounding the intercellular spaces. 
Dippel’s account of the history of the middle lamella in the 
wood and bast of higher plants is briefly as follows (pp. 570 ff.). 
The radial walls of dividing cambium cells are separated from 
one another by a lax, weakly refractive Zwischenmasse or 
Zwischensubstanz. This substance decreases in amount as we 
pass outward from the cambium layer into the differentiated 
wood and bast tissues, until it finally disappears, excepting at the 
angles formed by the junction of three or four cells. Remains 
of the cambium mother cell walls may occasionally be recog- 
nized in the Zwischensubstanz, which Dippel believes to be at 
least partially produced by their disorganization. Chemically, 
the Zwischensubstanz may consist of a union of pectose and callose, 
which is soluble under the conditions of cell wall development, 
