158 
FRANCIS E. LLOYD 
So long as the cell has not passed beyond the condition thus far described, 
the addition of water to fresh or alcohol-fixed material does not affect its 
internal topography, whereas when the secretion of mucilage has been 
begun this is not the case. Assuming however the contrary, that mucilage 
has already appeared, and providing that the cell is still immature, the 
imbibition of water from the surrounding milieu by the mucilage causes a 
displacement of the protoplast from the cell wall more or less complete.^ 
This is explained by the circumstance that material capable of a high degree 
of hydration now occupies the inner surface of the cell wall. It can now be 
shown that an inner zone of this wall, approximately half as thick as the 
whole, is in a more hydrated condition than the remaining cell-walls because 
it gives a deeper hlne coloration with iodine. The inner face of this zone is not 
optically definable but fades into a colorless substance, the mucilage. The 
amount of this present is indicated by the amount of displacement of the proto- 
plast from the wall. Usually the protoplasm will hold to the wall at several 
points, especially where pits occur, and when the mucilage becomes more abun- 
dant its swelling results in the somewhat bizarre appearance of an entire proto- 
plast compressed at the middle of the cell and connected by strands of proto- 
pasm with the wall at several or many points. The larger conspicuous 
strands have their distal place of attachment to the cell wall at or very near the 
middle points of the areas of contact of the contingent parenchyma cells. 
This appears clearly to indicate that the reason for adherence is the presence 
of the intercellular connections at these points, which are marked by wide, 
shallow pits. 
When the amount of mucilage arrives at or near to the maximum, the im- 
bibition of water permits its hydration to such an extent that the protoplast 
becomes crowded into an irregular echinate mass, the radiating protoplas- 
mic processes being either detached from the wall or variously torn asunder. 
The mucilage itself is now seen, but with some difficulty, to be laminated, 
the zonation being parallel to the cell wall but with curvatures toward the 
pits. This zonation, seen in Opuntia elatior by Cramer (fide Wigand, 1863, 
p. 149), is due to varying degrees of hydration (Walliczek, 1893) as appears 
from the fact that, when dehydrated with alcohol, internal syneresis occurs 
much more extensively in the more hydrated zones, which are then dis- 
coverable to the eye as zones of small spherical cavities of various sizes, 
but all minute. Such syncretic cavities may, however, be quite large, 
depending, in part at least , 6n the rate of dehydration, and probably also 
on the degree of hydration of the mucilage as a whole. The lamination is 
generally observable before or during the course of swelling, and is much 
more evident in Carnegiea gigantea. In this form the mucilage swells more 
slowly, and the loss of the marked lamination during increasing hydration 
In order to form a critical judgment of the condition of the mucilage cells, fresh sec- 
tions must be examined without the addition of water, as should also fresh and alcohol- 
dehydrated material with added water. 
