450 Ganong. — The Comparative Morphology of 
the columnar Cerei in their broad cotyledons, though these 
are less broad than in the Cerei, and in the very succulent 
hypocotyl, which is somewhat more elongated in this form. 
The epicotyl has eight ribs from the start, showing how old 
is the rib-forming habit. 
7. Genus Cephalocereus. 
C. senilis , Pfeiff. Figure 23. 
This genus merges with the last and with the columnar 
Cerei. In C. senilis (Fig. 23) the cotyledons are narrower 
than in the columnar Cerei, and the hypocotyl is relatively 
more succulent. The large size of the embryos is noticeable. 
8. Genus Eehinoeereus. 
E. caespitosus , Engelm. Figure n^in Engelmann, PI. XLIV. 
E. pectinatus rigidissimus , Engelm. Figure 24. 
E. phoeniceus, Lem. Figure 25. 
E. Engelmanni , Lem. Figure 26. 
E . procumbens , Lem. Figure 27. 
E . tuberosus, Poselger. Figure 28. 
This genus is very closely related to Cereus , though 
Schumann now considers it as well marked. It belongs 
nearest to the columnar Cerei, but to a division of the latter 
containing small forms. All forms in this genus are small and 
weakly armed. According to Schumann there are four sub- 
groups. One of these, including the erect forms and nearest 
to Cereus , includes E. pectinatus rigidissimus , phoeniceus, and 
Engelmanni (Figs. 24, 25, 26), which I have studied. The 
very broad cotyledons of C. pectinatus rigidissimus show the 
closest resemblance to the columnar Cerei, though the embryos 
are of much smaller size than in th egiganteus section. Of much 
larger size, and with the cotyledons somewhat less broad, is 
E. phoeniceus (Fig. 25), but it has the distinctive parallelism as 
to their bases so characteristic of Cereus. E. Engelmanni 
(Fig. 26) has the cotyledons much reduced and resembles 
more nearly some of the Echinocacti , and there is possibly 
some error in my materials. A second division of this genus 
