8 SmitH: THE HISTOLOGY OF CERTAIN ORCHIDS 
found fully developed in very young buds, showing that they are 
associated with actively growing regions. No slime cells in the 
process of development were found in the mature flowers. The 
region immediately surrounding the mucilage cells in young buds 
was characterized by actively dividing cells. All stages in the 
formation of mucilage were seen. The first indication that a 
cell will produce mucilage is the enlargement of the nucleus. 
The cytoplasm in such a cell is denser than in the neighboring 
cells and there is no large central vacuole. The cell has also 
enlarged somewhat. The measurements of cells which do not 
bear mucilage varied from 14 yp to 19 w in width by 26- 
22 wu. Those which are enlarged in preparation for producing 
mucilage are 22-29 pv in length by 22-26 w in width. The 
next stage in the development of the mucilage-bearing cell 
is the appearance in the enlarged cell of a small rather centrally 
placed vacuole. Before it has enlarged conspicuously a small 
bundle of raphides is formed in it. The raphides enlarge with 
the growth of the cell, which now stretches longitudinally. The 
average dimensions of such cells are 18.5 x 74 p. The average 
dimensions of the bundles of crystals in these cells are 14.8 u 
in width by 65.5 wu in length. The crystals are apparently 
suspended in the vacuole by strands of a substance which stains 
red with the triple stain and which also surrounds the crystal 
asathin sheath. This envelope about the bundle in the mature 
cell is enlarged into a knob-like mass at the end of the bundle, 
in which highly refractive drops may sometimes be seen. Drop- 
lets of the same character were observed occasionally over the 
entire surface of the bundles of raphides giving the sheath a 
curdled appearance. The raphides have practically attained 
their ultimate size before there is any indication of the homo- 
geneous yellow staining mucilage which finally almost fills the 
mature cell. The mucilage first appears as a thin layer inside 
the primordial utricle and surrounding the central vacuole. 
The mature cells have the following dimensions, in microns: 
Mature mucilage cells in bud 8 mm. Bundles of raphides in correspond- 
in length i 
Width Length Width Length 
a7 351 15 74 
185 16 67 
32 93 15 66 
37 266 19 63 
