VEGETABLE CYTOLOGY 
91 
Mucilage is stored as reserve food in the tubers of Salep and 
many other Orchids and also in the seeds of some species of the 
Leguminosae. 
Cell-content mucilage has been found in the leaves of Aloe, 
the rhizomes of Triticum, the bulb scales of Squill and Onion and 
in certain cells of many other Monocotyledons, especially those 
containing rap hides. 
Membrane mucilage has been observed in Barosma, Ulmus , 
Althcea , Linum , Astragalus , and Acacia species, in the Blue-green 
Algae, and many of the Brown and Red Algae. 
When mucilage is collected in the form of an exudate from shrubs 
and trees it constitutes what is termed a gum. Many of these gums 
are used in pharmacy, medicine and the arts. The three most im¬ 
portant from a pharmaceutical standpoint are: Acacia, yielded by 
Acacia Senegal and other species of Acacia ; Tragacanth, yielded by 
Astragalus gummijer and other Asiatic species of Astragalus ; and 
Cherry Gum, obtained from Prunus Cerasus and its varieties. 
Mucilage may be demonstrated in plant tissues containing it by 
placing sections of these in a deep blue solution of methylene-blue 
in equal parts of alcohol, glycerin and water on a glass slide, allowing 
them to remain in the solution for several minutes, then draining 
off the stain and mounting in glycerin. Those cells containing muci¬ 
lage will exhibit bluish contents. 
21. Fixed Oils and Fats.— These are fatty acid-esters of glycerin 
which are found in the vacuoles of cells or formed with the cell 
walls from which they may be liberated as globules upon treating 
sections with chloral hydrate or sulphuric acid or heating them. 
They are quite soluble in ether, chloroform, benzol, acetone and 
volatile oils but insoluble in water, and, with the exception of castor 
oil, insoluble in alcohol. „ They are readily distinguished from the 
volatile oils in that they leave a greasy stain upon paper which does 
not disappear. Fixed oils and fats take a brownish to black color 
with osmic acid, a red color with alkannin or Sudan III and a blue 
color with cyanin. In Vaucheria, the Diatoms and a few of the 
other Thallophytes, fixed oil is formed in the chromatophores in¬ 
stead. of starch as the first visible product of photosynthesis. In 
higher plants it is generally found in storage regions, such as the 
