45 # Ganong . . — The Comparative Morphology of 
material, nor do I understand the curious figure given for 
E . phyllacanthus by Zuccarini. 
In Malacocarpus I know only the figure of E. corynodes 
given by Zuccarini. The embryo has very small cotyledons, 
which are, however, prominent and pointed, on a nearly 
globular hypocotyl. 
In the important Thelocactus I have studied embryos of 
E. lophothele and E. Scheerii (Figs. 42, 43). Both have nearly 
globular hypocotyls, with very small rounded cotyledons, 
and in these respects approach very near to Mamillaria , 
which genus indeed these species, particularly E. Scheerii , 
approach very closely, as is shown by other considerations 
given in the systematic works. E. brevihamatus would be an 
interesting form to study in this connexion. It is well known 
that E. Scheerii shows clearly the furrow on the upper side 
of the tubercle which represents the drawing out of the 
vegetative point by intercalary growth of the tubercle in that 
region, and this feature becomes of great importance in 
Mamillaria. The earlier tubercles do not show it, but in the 
development of the epicotyl in E. Scheerii it is easy to see 
how this groove develops ontogenetically. The earlier 
tubercles show no trace of it, but after some twenty of them 
are formed, one appears with a tiny groove projecting slightly 
from the spine-cluster on the upper side of the tubercle ; 
the next shows this a little longer, and the next yet longer, 
and so on until the groove is complete. But it is not until 
much older tubercles than these are formed that the flowers 
first appear. 
The fine figure of E. Simpsoni given by Engelmann shows 
pointed and rather large cotyledons, and seems related more 
nearly to the Ancistrocactus group, though its replacement 
of ribs by tubercles would suggest that it belongs to the 
division Thelocactus. The melting away of ribs into tubercles, 
however, is a character which can readily reappear again 
and again, and need not indicate relationship ; and the close 
relationship of this species, emphasized by Engelmann, to 
E. intertextus , a ribbed species, confirms this. 
