Ranales , Rhoeadales , and Rosales. 717 
cotyledonary node the first plumular leaves show very well the ‘ double- 
ness’ often seen in the leaves immediately succeeding the cotyledons 
(Text-fig. 28). 
Arabis rosea presents a very perfect example of the diarch type 
in which complete root structure is present very high up in the hypocotyl. 
This structure bears no relation to the apparent collet. 
Aubretia Antilibani shows a detailed likeness to Arabis rosea. 
Sinapeae. 
Teesdalia nudicaulis is very similar to the preceding genera. 
Iberis tenereana (PI. LI, Figs. 13-16) is a good example of the 
general features of the type. One seedling shows particularly well the way 
in which the doubleness of the cotyledonary strand may be masked by 
early appearance of cambium, which by its activity between the two 
primary groups of phloem links these together with secondary phloem, with 
the result that the two original centres of phloem production are so obscured 
that they may be overlooked at this stage. At the base of the cotyledons 
the cambium is confined to the wings — that is, to the inside of the phloem 
groups, so that the bundle is obviously double. At this level in still older 
seedlings a further age effect is very well seen, namely, the obliteration 
of the central alternate protoxylem group, which gives the appearance 
of two separate bundles described by many writers (see de Bary and more 
recently Scott). 
Iberis sempervirens resembles Iberis tenereana very closely. 
Aethionema persicum. The transitional phenomena are similar to those 
of the preceding genera. The top of the hypocotyl shows very definite 
strands in the intercotyledonary plane, each having two or three lignified 
elements. These are continuous with the plumular midribs, which however 
are as yet in the undifferentiated desmogen state. The central protoxylem 
of the cotyledonary strands is obviously degenerating in the cotyledons, 
hypocotyl, and root. Secondary thickening has begun early, and partly on 
this account a rectangular-looking stele is found in the top of the hypocotyl 
which is slightly more elongated in the intercotyledonary than in the 
cotyledonary direction, and has four phloem groups arranged in pairs. 
Peltaria alliacea is characterized by the presence of root structure 
very close to the cotyledonary node. Very early production of cambium 
masks the degenerating protoxylem elements of the central position in the 
cotyledons except quite at the base, where cambium is not formed in 
the middle line. (Compare Iberis , &c.) 
Sisymbrium carpaticum conforms completely to the general type. 
Degenerating protoxylem is obvious throughout the seedling. One trico- 
tylous specimen was examined which formed a triarch root as in Cheiranthus 
Cheiri. 
