Igor] THE MIDDLE LAMELLA 7 
and so, for the most part, is absorbed into the cambial daughter 
walls. The cambial cell walls (p. 575), that is the cell walls 
of the cambium mother* and daughter cells, are composed 
of pectic acid, which, at least after the transformation of 
these walls into an “intercellular substance,” exists largely in 
the form of’ calcium pectate. As the cambial daughter cells are 
transformed into bast and wood tissue, the primary cell walls, 
consisting of pectose and cellulose, are deposited next to the 
now apparently simple cambial walls. These latter now undergo 
a transformation, forming an ‘intercellular substance,” or K7¢t- 
substanz, which, through a loss of water and the extension in 
length of the radial walls, becomes so thin as to be in most 
cases invisible except after special treatment. It is, besides, 
fused into apparently intimate connection with the primary cell 
walls. This combination of the intercellular substance and 
the primary cell walls forms the middle lamella of mature 
tissues, against which in the process of development secondary 
thickenings are deposited. The continued existence of the 
“intercellular substance” as a middle plate ( Theilplatte) of the 
middle lamella Dippel demonstrates by the action of the wall 
layers upon polarized light, as well as by treatment with various 
macerating and staining reagents, notably ruthenium red. 
Dippel’s peculiar view, developed in connection with his 
studies on the algae, that cell division is.accompanied by the 
formation of a new cell wall entirely enclosing each daughter 
cell, has doubtless influenced his account of the development of 
the middle lamella in the higher plants. For if this were the 
case in the predominantly radial growth of cambium cells, the 
result would be to leave, between the radial walls of the newly- 
formed daughter cells, the old mother cell walls, which, if they 
became disorganized, would form a Zwischensubstanz such as 
Dippel describes. The tenability of this view of the origin of 
the Zwischensubstanz will be discussed hereafter. 
*Here there seems to be a contradiction, for Dippel has already spoken (p. 575) 
of the cambium mother cell walls as being disorganized toform the Zwischensubstanz 
of the daughter cell walls. 
