7 26 Thomas. — Seedling Anatomy of Ranales, &c. 
four phloem groups, which may probably be taken as an indication of 
tetrarch relationship. 
Leguminosae. 
Ceratonia siliqua , Acacia dealbata (see Compton 1 ), Medicago mar- 
ginata, and M. rutitexta . These species show hypocotyledonary structure 
which is essentially similar to that of Primus persica , that is to say, 
four protoxylem strands are present alternating with four phloem 
groups with metaxylem to the inside. These strands of phloem and 
metaxylem are more or less twin structures according to the individual. 
This difference corresponds to some extent to the degree of freedom of the 
lateral strands in the base of the cotyledon. Thus in Ceratonia siliqua they 
become independent at the node, while in the other species they are massed 
together at the node, so that these species conform to the ‘ Althaea * or 
‘ Anemarrhena ’ type (see PI. LI, Fig. 23). The root is tetrarch, as in so 
many Leguminosae. 
The cohort of the Rosales may perhaps be said to present the widest 
range of seedling anatomy of the three cohorts considered in this paper. 
It is impossible to assign a position to the tetrarchy of the Pittospora- 
ceae without some knowledge of the origin of the four cotyledons. 
If they are derived from the dicotyledonous condition, two methods 
are possible: (1) bifurcation of two original cotyledons; (2) suppression of 
internode between cotyledons and plumular leaves which, in the language of 
Hill and de Fraine, 2 have been thus ‘promoted’ to be cotyledons. 
In the first case the tetrarchy would necessarily be a modification of 
diarchy, in the second case probably of tetrarchy. 
I know of no morphological evidence bearing upon this question. So 
far as collateral evidence goes, the only other member of the Pittosporaceae 
examined, namely Sollya, is diarch, and the neighbouring order of the 
Hamamelidaceae shows in Liquidambar the curious separation of the halves 
of the cotyledonary strand by means of a secretory canal ; it is probable 
therefore that Pittosporum shows that modification which leads to the 
production of poles in the diagonal planes (see Calycanthus). 
Within the Rosaceae it is the Pomoideae section which includes the 
greatest range of type, the diarch forms of which might be accountable for 
on the habit hypothesis, but the variations in the genus Pyrus do not lend 
themselves to this interpretation. They illustrate very well the comparative 
constancy of the hypocotyl, which may be associated with very different 
arrangements in cotyledons and root. 
1 Compton, R. H. : An Investigation of the Seedling Structure in the Leguminosae. Journ. 
Linn. Soc. Bot., vol. xli, 1912. 
2 Hill and de Fraine: On the Seedling Structure of Gymnosperms, II. Ann. Bot., 1909, 
vol. xxiii. 
