de Fraine .— The Seedling Structure of certain Cactaceae. 159 
hypocotyl, are of the ‘ barrel * or spindle type, and are very sharply marked 
off from the protoxylem (Fig. 19). 
Mamillaria rhodantha , Link and Otto. One of the seedlings examined 
showed a transition almost precisely similar to that described in M. multiceps , 
but the others differed. 
In these last the cotyledonary bundles (c x , c 2 ) appeared at the node; 
Fig. 19. Mamillaria imdticeps. Protoxylem elements and ‘ barrel ’ tracheides. x 420. 
in addition to them were two tubercle-strands (t 1} t 2 ) and two epicotyle- 
donary traces (e), and, very shortly, four smaller epicotyledonary strands 
were differentiated. Fusion of these bundles took place in the manner 
indicated in Diagram 15, Figs. 1 and 2. At this stage the cotyledonary 
phloem bifurcated, and rotated through an angle of 90°, thus leaving the 
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Diagram i 5. Mamillaria rhodantha. 
protoxylem exposed. The remaining four bundles present in the hypocotyl 
moved outwards and fused laterally with the cotyledonary bundles 
(Diagram 15, Figs. 2 and 3). A few large metaxylem elements begin 
to develop at this stage between the protoxylem and the phloem, so that 
there are present two strands similar to those figured in Diagram 14, Fig. 5. 
The remaining details of the transition are similar to those of M. midticeps. 
Mamillaria meiacantha , Engelm. These seedlings showed a transition 
which in all essential features resembled that of the last described individuals 
of M. rhodantha. 
Mamillaria ceittricirrha , Lem. This species showed some slight 
