STEWART: MUCILAGE FORMATION IN THE CACTI 159 
first attempted cytological study of the cacti. He noted that the 
contents of the parenchyma cells was primarily “starch or muci- 
lage in globules.” Both were almost always surrounded with 
chlorophyll. In almost all species which he studied he reported 
that he found two to six times enlarged cells distributed in the 
cortex and in the central parts of the stem, all of which were totally 
filled with a vegetable jelly with a characteristic type of organiza- 
tion. These mucilage-filled cells he said he could not find in 
Rhipsalis rhombea, but in their place he found large cells filled 
with starch. 
Between this work of Schleiden (20) in 1837 and that of Lauter- 
bach (8) in 1889, no very full study of the mucilage of the cacti is 
reported. Cramer (2) described the slime of the cacti arising as a 
thickened layer on the cell wall, thus proving, as he held, its close 
relationship with cellulose. He found these continuous thickening 
layers in especially large single cells. He believed that by rupture 
the wall layers became irregular and showed such a structure as 
Schleiden (20) described. 
Schacht (18) studied old stems of Opuntia Ficus-indica and 
reported gum-like tragacanth contained in canals. He believed 
that this gum arose as the result of a disorganization of the cell 
wall. Wigand (24) observed that certain parenchyma cells in 
the cacti, which were of somewhat greater diameter than their 
neighbors, were filled with a homogeneous colorless slime. De 
Bary (3) noted that this mass of mucilage had the structure of a 
very thick, abundantly, and delicately stratified cell wall. He 
concluded that it was the cell wall thickened at the expense of the 
internal cavity of the cell. 
From his investigations Lauterbach (8) was led to believe that 
there are two methods by which the mucilage is formed, one 
holding true for Opuntia, and the other for the remainder of the 
cactus groups. In the Opuntia the mucilage arises in a cell 
containing a small crystal of some oxalate. This crystal, as he 
thought, seemed to stimulate the growth of the cell. Later the 
nucleus and crystal might appear suspended on strands of cyto- 
plasm in the midst of the cell and mucilage would then begin to 
appear in the periphery of the protoplasm. 
In the other cacti he held that the mucilage also arose in the 
