de Fraine .— The Seedling Structure of certain Cactaceae. 131 
hitherto been undescribed among Dicotyledons, with the possible exception 
of Eranthis and Podophyllum. 
Opuntia imbricata , D.C. In all essential features the transition in this 
seedling resembles that in O. Ficus-indica. 
Opuntia Tuna , Mill. 
Series A showed a type of transition such as is found in O. Ficus-indica. 
Series B had at first a tetrarch root, produced in the same way as in 
Series A ; but, at a lower level, this changed to a pentarch structure in the 
following manner. 
The intercotyledonary protoxylem group (px 3 + px^ in Fig. 4 a) 
Fig. 4 b. Opuntia Tuna. Series B. x 220. 
appeared to be about to die out, when it was reinforced by a branch of 
xylem from px{ (pxf ; simultaneously px Y gave ofif another branch 
( p x P), and finally a fifth phloem group (ph l ) arose between px 1 and px± 
(Fig. 4 b) ; in this way the pentarch structure was completed. 
Series C had a transition which was a slight modification of the 
Anemarrhena type. Two V-shaped bundles passed into thehypocotyl from 
the two cotyledons, the arms of the V very rapidly opened out, and the 
protoxylem which occupied its apex divided ; half formed the exarch proto¬ 
xylem group of the cotyledonary root-pole, the other half passed inwards 
