164 STEWART: MUCILAGE FORMATION IN THE CACTI 
bition experiments with joints of Rhipsalis, I have found that the 
greatest swelling in a majority of cases takes place in the apical 
region, the region of growth and of abundant mucilage cells. 
We have then in the cacti a transformation of the content of 
many cells in the growing regions into a mucilage which, by ab- 
sorbing water, may simulate true growth and may be of importance 
in conserving and regulating the supply of water for the growing 
cells themselves. As to the method of formation of the mucilage, 
as I have noted it in the cacti and more particularly in Opuntia 
and in Rhipsalis, it is the nucleus and cytoplasm that are the active 
agents. Apparently the cell wall is at no time involved in the 
process. The mucilage comes from the cytoplasm and the for- 
mation begins between the cell wall and the protoplasm, as Longo 
(11, 12) points out. As the mucilage increases the nucleus and 
cytoplasm decrease in size and may entirely disappear, leaving 
the enlarged cell completely filled with mucilage. 
That all resins, gums, and mucilages are similarly formed is in 
no sense suggested, but it is of interest that we have in these 
mucilage cells of the cacti a method of secretion much more like 
that of the gland cells of animals than the more familiar method 
by a resinogenous layer of the cell wall as found in many trichomes. 
In concluding, I wish to express my gratitude to Dr. R. A. 
Harper of Columbia University, under whose direction this work 
was carried out, for his helpful criticisms and suggestions. 
DEPARTMENT OF BOTA 
COLUMBIA oie 
LITERATURE CITED 
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2. Cramer, C. Ueber das Vorkommen und die Entstehung einiger 
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3. De Bary, A. Vergleichende Anatomie der Vegetationsorgane der 
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