the Embryos and Seedlings of the Cactaceae. 461 
M. Sempervivi, DC. Figure 47. 
M. Goodridgiif Scheer. Figure 48. 
M. glochidiata, Mart. Figure in Zuccarini, PI. I, Fig. I, 4. 
M. tentaculata , Link and Otto. Figure in Pfeiffer, PI. XVI, Fig. 8. 
This very large genus contains the smallest species of the 
family, and consists of globular to short cylindrical forms 
with spirally-arranged tubercles (and never ribs), with spine- 
clusters at the ends of the tubercles and flowers in their axils. 
In one division the tubercles have a longitudinal furrow along 
the upper face, and these connect with the furrowed Echino- 
cacti of the division Thelocactus. In the other division the 
furrow is wanting. The explanation of its presence in the 
one group and its absence in the other I have elsewhere 
given 1 . 
Throughout this genus the embryos show a very succulent 
and usually nearly globular hypocotyl, with cotyledons always 
small, sometimes indeed so small as to have been considered 
wanting. They are usually rounded, but sometimes more or 
less pointed. 
In the division with the furrow I have had seeds only of 
M. elephantidens , which have produced an embryo of re- 
markably large size (Fig. 45), with an elongated hypocotyl 
and rather broad rounded cotyledons, suggesting the Cephalo- 
cactns division of Echinocactus , with which however it is 
scarcely at all possible that Mamillaria has directly any 
affinities. Since Goebel’s figure of M. latimamma shows the 
same elongated hypocotyl, it is possible this is a common 
characteristic of this division. In this connexion the embryos 
and seeds of M. macromeris would be of especial interest. If 
this furrowed division of Mamillaria is derived, as other 
considerations seem to show that it is, from the Thelocactus 
division of Echinocactus , then the large size and elongated 
hypocotyl must be re-acquired and not primitive, for neither 
character appears in E. S cheer ii (Fig. 43), a good represen- 
tative of Thelocactus . The epicotyl in M. elephantidens 
develops the clusters spirally on short tubercles, with no 
1 In Flora, op. cit., p. 75. 
