426 Ganong. — The Comparative Morphology of 
a few seedlings are described and sweeping conclusions drawn 
upon altogether too scanty evidence. There are of course 
other references, including those in inaugural dissertations by 
Kaufholz and Michaelis, and in the £ Monatsschrift fur Kakteen- 
kunde/ but they are of minor importance. One characteristic 
of nearly all of the figures in the various works I have cited is 
this — they show the epicotyl very well developed, but not the 
form in its true embryo condition ; . and hence they are less in- 
structive in the present study than would otherwise be the case. 
Materials. 
The value of a study like the present depends very largely 
upon the authenticity of the seeds used ; and the difficulties of 
obtaining and raising them are great. I have tried first of all 
to obtain seeds collected in the field by botanists who are 
known to be particularly well acquainted with their own flora, 
and for seeds collected under these conditions I am greatly 
indebted to Mr. S. B. Parish of San Bernardino and to 
Professor J. W. Tourney of the University of Arizona, both 
of whom have most liberally responded to my troublesome 
requests. Other materials have been sent me by Mr. C. R. 
Orcutt of San Diego, Mr. W. Fawcett of Hope Gardens, 
Jamaica, and by a few others, to all of whom I extend here 
my sincere thanks. Next to material from this source, I have 
valued that obtained from Botanic Gardens, particularly from 
those of Palermo and Florence, where the Cactaceae grow 
under conditions far more nearly natural than in the northern 
gardens, where indeed many kinds do not bloom at all, or 
only rarely and in single specimens. Finally, I have obtained 
some seeds from dealers, but in general I have only trusted 
the correctness of the naming of the seeds I have bought 
when they grew into seedlings recognizable as of that species, 
or when from two distinct sources I have obtained what are 
plainly the same seedlings ; and indeed I have tried to apply 
this test also to those obtained from Botanic Gardens. One 
source of error in raising them must be guarded against — 
