THE ORIGIN AND NATURE OF THE MUCILAGE IN THE 
CACTI AND IN CERTAIN OTHER PLANTS* 
Francis E. Lloyd 
The increasing interest in the role of emulsoids in the economy of the 
plant, especially in that of the growth processes, has indicated the necessity 
of re-examining them from the more recently taken point of view exemplified 
in the work of Borowikoff, Long, MacDougal,. Spoehr, and others.^ More 
specifically regarded, the question of the relation of alterations in the volumes 
of emulsoids due to changes in the acid and salt content of the tissues, and 
the effect of these alterations on the volume of the plant body is one of 
paramount importance, and is particularly to the fore at the moment. ^ 
In a good many plants the presence of very considerable quantities of 
mucilages and "gums" has of course long been a matter of common knowl- 
edge and has been much investigated, chiefly from the point of view of the 
histologist and pharmacologist^ with only side glances at their physiological 
contacts, leaving much to be said from the present point of view. The 
following account is confined principally to the mucilage of Opuntia in situ, 
having regard to its origin and distribution, coupling therewith some notes 
on the comparable conditions found in Tilia, Malva, and Astragalus gummifer 
(tragacanth). 
Distribution of Mucilage Cells 
The mucilage in Opuntia originates within, and is normally confined to, 
definite large cells (mucilage idioplasts) scattered throughout the paren- 
chyma, both medullary and cortical. Their absolute number is correlated 
with the species. Their distribution in the cortex and medulla differs also 
in different species. Thus, in Opuntia sp. (a species obtained from Dr. 
D. Griffiths and now in the garden at the Coastal Laboratory of the Car- 
negie Institution of Washington) none are found within 2.5 mm. of the 
epidermis of the joints, though they occur more closely thereto in the leaves. 
In Opuntia Blakeana, however, they lie very near the epidermis. For this 
reason it is practically possible, in the former species, to cut sections of the 
chlorenchyma parallel to the epidermis which when allowed to lie in water 
give off no mucilage. There is observable no mucilage identical with that 
of the mucilage idioplasts in any other cells, though it is not at the moment 
denied that there may be a very small amount of hydrophile colloid in the 
vacuoles of the ordinary parenchyma cells. 
* A subvention from the Cooper Fund for Medical Research of McGill University is 
hereby acknowledged. 
1 For citations see MacDougal and Spoehr, 1917. 
2 MacDougal and Spoehr (/. c); Lloyd, 1917, 1918a. 
3 See Tschirch, 1884. 
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