at 7 4 | ?. > ie’ & . ey Cm a4 Foo a Ct ®Sy rat ve Ov@ Pale! ar 
Jt fon Fe at ’ Ber t v7) ay ay AE ak ters i Wk Bee 7? ean 
' s Fa eae Ae “ 2 Z ene 
A 1 
36s Structural and Physiological Botany. ony e ae 
that it can be artificially destroyed only by chemical re- 
agents which dissolve the outermost layers of the cell-walls : 
themselves. It nevertheless happens very frequently that, — | 
in consequence of the unequal growth of adjacent cells, the 
cell-walls which have already coalesced again partially or 
entirely separate from one another, so that a cavity or zater- 
cellular space is formed between these cells (Figs. 60, 63). 
The form and arrangement of these small intercellular spaces | 
differ greatly in different plants, and in different parts of 
the same plant. They occur, for example, between the 
spherical cells of certain groups, where they form together 
a system of zntercellular passages, which often increase ~ 
into capacious air-cavities, air-canals, or large open spaces. 
The causes which co-operate in the formation of these in- | 
tercellular spaces may be very various ; in addition to the — 
- separation of cells previously united, a dismemberment and | 
subsequent drying up of dead cells may be especially 
mentioned. 
here is no special substance uniting and uniformly cementing 
_together the individual cells ; but if groups of thick-walled cells are 
examined, it is generally found that 
the contiguous cells are connected ~ 
together by a uniform median layer 
apparently common to the two cells. 
It was the figuring of this structure 
(Fig: 57) which originated the idea. 
of a peculiar ‘intercellular sub- 
stance’ not belonging to the cells ;_ 
but a more exact investigation, 
especially of the development of 
the groups of cells, shows that even. 
in these cases there is no indepen- 
Fic. 57.—The so-called ‘ intercellular sth methan layer, but ‘fathers 
substance,’ as delicate. lines which region where a coalescence has, _ 
le aml ara ner es taken place of contiguous cell-walls 4 
ipo which may have undergone in the 
course of their growth some important change in their chemical nature. : e ‘- 
~ 
