158 STEWART: MUCILAGE FORMATION IN THE CACTI 
from the cell wall. He noted that at first these gum cells con- 
tained starch grains, many of which appeared corroded. 
Prillieux (17), in the gummosis of fruit trees, claims that gum 
may appear in cells whose walls do not show a trace of disorganiza- 
tion. The starch grains simply disappear and small masses of gum 
take their place. Haberlandt (5), in his treatment of the anatomy 
of cells containing slime from a morphological viewpoint, considers 
the slime masses in Malvaceae, Marchantiaceae, Cactaceae, and 
Lauraceae to be a very strongly thickened and finely stratified 
cell membrane. According to Haberlandt (5), in such cases the 
primary cell wall, as a rule, does not degenerate. 
In 1893 Walliczek (23), working under Tschirch, concluded 
that there were cell content slimes as well as membrane slimes, 
but that cell content slime had been proved only for Orchis and 
Symphytum. He found that the cell content slimes appeared as 
homogeneous masses, while the membrane slimes were stratified. 
The following year Schilling (19), working on the question of 
slime formation in water plants, decided that slime building went 
on at the expense of the cell wall and that at the end of the process 
only a very thin shell was left about the cell. | 
Butler (1), studying gummosis in fruit trees, accepts the view 
that the process of gum formation is a degeneration of the cell 
wall. The essential factors are relative rate of growth and water 
supply. Dissolution begins in the secondary lamella and almost 
coincidently in the primary membrane, and the cell contents are 
at no time actively concerned in gum formation. _ 
We now turn to a consideration of the investigations that have 
been made relating to the formation of mucilage in the cacti. 
These plants have been rather exhaustively studied for many 
years but so far comparatively little cytological work has been 
done upon the group. In most of the forms mucilage is very 
abundant. The question as to the method of its formation was 
discussed first by Meyen (14) in 1837. He reported that he 
found mucilage in the intercellular spaces of the cacti and in some 
cases he found mucilage ducts in great numbers. He concluded 
that a direct transformation of cell contents into mucilage took 
place and showed a figure with cells filled with mucilage. 
Two years later Schleiden (20) published the results of the 
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