Ranales , Rhoeadales, and Rosales. 
7i5 
The extreme simplicity of this arrangement is due to the continuity of 
two strands of alternately placed exarch protoxylem throughout the 
seedling from the diarch root to some region in the cotyledons where more 
or less gradually the collateral arrangement is assumed. These strands are 
continuous with the central bundle of the series of collateral strands of the 
lamina, all of which are massed with the central at some point usually in 
the blade, but one independent lateral bundle may be met with in the 
petiole on each side of the 'central strand (e. g. Liinaria biennis). The 
existence of the alternate exarch or mesarch protoxylem group is frequently 
almost or quite non-identifiable on account of the degeneration changes 
which take place in these elements, leading to their obliteration in cotyledons 
and top of hypocotyl at an early age. 
Cheiranthus maritimus. The structure is in essentials quite similar to 
that of C. Cheiri. No laterals were seen in the petiole. 
At an early age the primary protoxylem is degenerated but usually 
still discernible as crushed streaks, while a few cambial divisions are to be 
observed. The first plumular leaves are opposite each other and alternate 
with the cotyledons. Their single central strands are essentially similar 
to those of the cotyledons, in that they are markedly double, consisting of 
a central group of protoxylem alternating with two centres of phloem 
formation. One lignified element which is continuous with the strand of 
the rudimentary first leaf may be found in the upper part of the hypocotyl 
at an age when the plumule is not obvious to the naked eye. 
Erysimum pulchellum. The transition features in this species are very 
similar to those in Cheiranthus. 
Alyssum rostratum. In the seedlings examined there are slight devia- 
tions from type in detail. Thus the protoxylem is scattered and not very 
obvious in the upper part of the hypocotyl, and even in the diarch plate it 
is crushed and degenerate-looking. This is no doubt only an extreme case 
of early degeneration of the protoxylem, as it is more marked in the older 
seedlings and is correlated with very precocious development of the 
cambium, the activities of which are very manifest even in the youngest 
seedlings. 
Alyssum maritimum , as described by Chauveaud, 1 seems to be quite 
similar. 
Anastatica hierochuntina. The anatomical arrangements are those 
characteristic of the group, and show the usual features of the diarch type. 
Malcolmia littorea presents a good example of the common arrangement. 
Degeneration of the protoxylem takes place at an extremely early age, as 
was far advanced in the seedlings examined, which were still very young 
as judged by internal as well as external marks. 
Matthiola tricuspidata (Text-fig. 26). Normal seedlings show the 
1 Loc. cit., 1911. 
