2 SMITH: THE HISTOLOGY OF CERTAIN ORCHIDS 
Gardner and Ito (1888) believe that the mucilage in the 
fern hairs of Blechnum occidentalis and Osmunda regalis isa 
product of the cell contents and that it is secreted as drops in 
the cytoplasm until the protoplast is exhausted, only a thin 
layer of the cytoplasm remaining. 
Groom (1893) notes in a discussion of bud protection in 
dicotyledons: “The employment of a hygroscopic substance’ 
like mucilage is an admirable means of controlling the water 
supply of an organ for two reasons; first, the osmotic power of 
a solution increases with the concentration of the solution. 
Therefore, when the bud is in the greatest danger of losing all 
the water; when the temperature is high and a considerable 
amount of water has been evaporated from the mucilage, the 
remaining water is held most firmly, and a supply of water is 
absorbed most fiercely.’’ He ignores the relation of the colloidal 
character of the mucilage to the imbibition of water. Were the 
principle of osmosis the only one involved here, the cells of the 
young buds would need to be vacuolated, as mucilage cells are 
predominantly reported not to be. 
Tschirch (1889 and 1908) distinguishes between cellulose 
slime and true slime and gums. He further differentiates them 
under the headings: epidermal — (Cydonia, crotaiaed and Lonne 
seeds), slime of the outer wall ( 
slime of the intercellular spaces Oc ilia, Malvdedac, Laminaria), 
cell content slime (Orchis tubers), schizogenous excretions 
(cycads, Aralia, Laminaria), and lysigenous excretions (Acacia, 
Prunus, Sterculia). In some cases he found empty slime cells 
which he took as an indication that the contents had been taken 
up again in the metabolism. The resins, he says, originate in a 
special layer of the wall, to which the material for making resin 
is brought, and calls this the resinogenous layer. 
Walliczek (1893) distinguishes gums, epidermis slime, cell 
membrane slime, and cell content slime. Of this last type of 
mucilage in connection with the Polygonaceae he says that he 
found slime in cells bearing raphides whose development here 
as in the case of all other such slimes is not certainly known. 
The forms which he studied did not contain such slime, so he 
has left this question as he found it. He confines his research 
to the slime in the vegetative organs, especially the epidermal 
cells of the leaves and the inner tissues of the vegetative organs, 
