134 de Fraine .— The Seedling Structure of certain Cactaceae. 
core of xylem resulted. In this seedling three cotyledonary bundles, 
by a branching of the xylem into three, have given rise to a hexarch root. 
Opuntia albicans , Sal m-Dyck. Only two seedlings of this species were 
obtained for examination, and in all essential characters of the transition 
they resembled O. slricta, Series B. 
Opuntia maculacantha , C. F. Foerst. A ‘ double 5 bundle passes into the 
hypocotyl from each cotyledon (Diagram 3, Fig. 1), and during the passage 
tfrrough the cortex the phloems, carrying with them the metaxylem, move 
further apart and leave the protoxylem more or less isolated. No sign 
of any branching of the protoxylem occurs, and the remaining two poles 
of the tetrarch root originate by the development of tracheides at A and B 
(Diagram 3, Fig. 2). 
& 
A * * B 
■0 
t ? § 
1 
2 
3. 
Diagram 3. Optmtia maculacantha. 
A few metaxylem elements are contributed to these two xylem groups 
by the cotyledonary metaxylem strands lying on either side. As in 
O. stricta. a few large barrel tracheides develop in the centre of the axis 
towards the hypocotylar base, but they do not long persist. 
Opuntia Pseudo-tuna , Salm-Dyck. The transition in the only seedling 
of this species available for examination took place as in O. mactdacantha ; 
it is somewhat complicated, however, by the considerable number of 
secondary tracheides present, for much secondary thickening had taken place. 
It further differed from 0. mactdacantha in the complete absence of £ barrel ’ 
tracheides. 
NOPALEA. 
Nopalea n. sp ., Rose. Of this genus the seed of only one species ger¬ 
minated, and judging from this example the seedlings bear a very close 
resemblance to those of the genus Opuntia , with the exception that the 
difference in size of the two cotyledons is much more marked in Nopalea 
than in Opuntia , or indeed in any other genus ; further, the seedlings show 
a slight advance in succulence (Fig. 6). 
