SMITH: THE HISTOLOGY OF CERTAIN ORCHIDS Ii 
that the region of the raphides is a formative one since the 
envelope of the needles stains differently from the mucilage 
about it, and that drops of still different character are some- 
times seen in the mass of material at the ends of the bundles 
as well as along their surfaces. The size of the crystals changes 
less during the life of the slime cell than the amount of mucilage 
does in the same period as a reference to the measurements of 
raphides and mucilage cells show. The normal appearance of 
the nucleus also indicates a living and active condition in the 
slime cell up to its mature condition. If the formation of muci- 
lage in these slime cells is a continuous process during the life of 
the plant organ in which the cell occurs, the manner of secretion 
may be compared to that in the gland cells of animals which 
secrete continuously or periodically. 
MacDougal (1920) claims that the measurements of variations 
in length and thickness of the succulent leaves of Mesem- 
bryanthemum Phaseolus and Opuntia yield ample evidence 
that the fluctuations in their growth show a direct relation to 
the hydration capacity of the growing cell masses, and that 
the high hydration capacity of Opuntia is due to the mucilage 
_ which it contains. The source of energy in hydration he at- 
tributes to the unsatisfied attraction of molecules or particles 
or ions bearing electrical charges. Polysaccharides, he says, 
appear to determine the water relations of living matter. He 
further says, “‘Growth consists in increases in volume of masses of 
living matter, usually but not invariably accompanied by ac- 
cretions of material other than water to the colloids of the proto- 
plasm.”” In the early stages of mucilage formation in the cells 
of A spasia sp., just as Miss Stewart has shown for the cacti, 
there is obviously an accretion of material other than water 
as the increased size of the cell completely filled with dense 
cytoplasm proves. The transformation of this cytoplasm into 
slime may be a process of hydration and involves the imbibition 
of water from adjacent cells. If the process is simply one of 
imbibition of water it might better be regarded here as a de- 
generative rather than a growth process. As noted, however, 
my preparations show that the nucleus maintains its organi- 
zation intact to the end. There is also a well-developed cytoplas- 
mic primordial utricle in the mature slime cell, so that in my 
opinion we have here the case of a true secreting cell in which 
