the Embryos and Seedlings of the Cactaceae . 469 
embryo, for the transition from epicotyl to embryo forms 
a barrier against which the crests of the waves are broken, 
and behind which only the influence of the ground-swell, as it 
were, is felt. It is the condition of these waves at this moment 
which gives us the present embryology of the family. 
Phylogeny of the Genera. 
We may now summarize what the preceding facts indicate as 
to the phylogeny of the genera. Taking them all into account, 
together with others drawn from the comparative anatomy 
of the adults, and to some extent others from the floral and 
fruit anatomy, the relationships appear to be as expressed 
in the following diagram. The outline of the main trunks 
and branches is intended to express the appearance of the 
whole group as it appears to us at the present day, while 
the axial lines are intended to represent the probable historical 
relations of the different genera, their place and relative time 
of origin from one another. 
All considerations show that Pereskia is nearest to the 
original stem-form of the family, and that Opnntia is derived 
from it, though the connecting forms still existing make of 
them a single trunk. From Opnntia came off Cereus , and 
our columnar Cerei are nearest to the primitive form as their 
cotyledons show, though the original Cerei must have been 
somewhat tubercled after the manner of Opnntia rather than 
strongly ribbed. From columnar Cerei came off in succession 
Echinopsis , Echinocerens , and Pilocerens , and from the last 
Cephalocerens. Well down in the stem of the columnar Cerei 
came off the climbing forms, giving another incipient genus, 
and from these came first of all Pfeijfera, with its early 
branch Rhipsalis, and later Hariota , and Phyllocactns with 
its branch Epiphyllum. From the columnar Cerei again, but 
low down and near Echinopsis , came off Echinocactus , which 
soon gave off as a branch the furrowed forms which gradually 
changed from the ribbed to the tubercled forms. These 
tubercled Echinocacti, with their furrow, gave rise to the 
