40 BOTANICAL GAZETTE [JULY 
The particular value of Ginong’s terse and concise descrip- 
tion of the fibrovascular system lies in the last clause, ‘‘the 
whole system conforming closely to the external form, and fol- 
lowing its morphological changes.” Upon this fact depends the 
usefulness of internal structure as evidence of systematic value, 
a point which this writer thus recognizes, and one which I feel 
that I cannot too strongly insist upon. Schumann gives a 
slightly fuller account of the vascular system, noting the pres- 
ence of annular and spiraled ducts, especially in young bundles, and 
their subsequent replacement by the various tracheids. This is 
also the statement of the fact that a regression toward more prim- 
itive conditions is taking place, by the substitution of elements 
of a less highly developed character. In this particular espe- 
cially considerable variation is shown, offering, together with the 
methods of bundle-branching and anastomosis, a very fruitful 
field for research from a systematic point of view. Annual or 
periodic rings are not always absent, as will be shown; in fact, 
in one form I have examined they are peculiarly marked. 
The work presented in this paper was done on fresh material 
collected in the vicinity of Tucson, Ariz., during December 1900, 
and examined immediately at that place. Opportunity was thus 
given to study the plants in their natural habitat, a very valuable 
advantage in dealing with physiological phenomena. 
CrREUS FENDLERI Engelm.—The hypoderma is compara- 
tively thin, of about three layers of cells; the cuticle is thick as 
usual; there are no crystals in the epidermis, only an occasional 
one occurring in the deeper cells of the hypoderma. The assim- 
ilative cells are large and fairly elongated, those nearest the sur- 
face containing the most chlorophyll, those toward the center 
grading into a very thin-walled parenchyma also slightly chloro- 
phyllous, and filled with an intensely stringy and slimy mucilage, 
which, by taking stains readily and by preventing dehydration, 
renders any delicate manipulation of sections upon fresh tissues 
out of the question. It is by this means that the plant is able 
to hold water so persistently. In the parenchyma are imbedded 
the bundles, slightly separated from each other in most cases, 
