SEEDLING STRUCTURE IN THE LEGUMINOSJE. 81 
(cf. Urban, 1873, p. 33). In Ononis biflora, and also in other species of this 
genus (De Candolle, 1825, p. 86), the cotyledons exhibit the very rare 
condition of pronounced hairiness. There is often a short one- or two-sided 
cotyledonary tube. 
There is some variation in the symmetry of the vascular structure 
within the tribe, and also within single genera and species; moreover, 
individual seedlings show differences in symmetry at different levels. In 
the majority of cases a tetrarch structure occurs in some part of the 
hypocotyledonary axis, the only exception definitely known being Ononis 
biflora, a plant which exhibits in its scedling structure a relationship to the 
Genisteæ also evinced by floral and vegetative characters. The other species 
of this genus examined, O. rotundifolia, while showing some kinship with 
the Genistez, is more conspicuously related to the other Tritolicæ. 
In some cases the root is tetrarch throughout, e. g., Medicago tribuloides, 
Trigonella Fanum-greeum, and some seedlings of T. gladiata ; but it is more 
usually triarch. In the majority of cases this triarchy is transformed to 
tetrarchy at a higher level (usually in the collet region) by the division of a 
phloem and the appearance of a new protoxylem between the two halves; 
the new xylem being in the intercotyledonary plane. The cotyledon traces 
may be derived from the tetrarch structure in one of two ways: the inter- 
cotyledonary xylem may divide in half along the minor axis of the stele, and 
each cotyledon will then receive a polar xylem and two half-lateral xylems ; 
this happening in most cases: or the intercotyledonary protoxylems may 
disappear completely, leaving the polar groups from which alone are the 
cotyledon traces organised ; this being observed in Ononis rotundifolia and 
Medicago turbinata. In these latter cases the root is sometimes triarch ; 
and consequently we find the curious phenomenon of a protoxylem confined 
entirely toa more or less limited range of the hypocotyl (in O. rotundifolia, for 
instance, sometimes only about 3 mm. long), and prolonged neither into the 
root nor into the hypocotyl. Ina single species, viz. Melilotus arvensis, the 
structure is similar but for the complete absence of the fourth protoxylem, 
triarchy passing directly to diarchy. 
The cotyledon traces are of a similar type throughout the tribe, consisting 
of a small crushed median protoxylem row flanked by a pair of oblique or 
collateral bundles ; the tetrarchy of the upper part of the hypocotyl of many 
species is not connected with the formation of lateral bundles at the base of 
the cotyledon, but is only revealed by the presence of small crushed vessels 
towards the edge of the collateral bundles. 
The level of the transition is high throughout, with the exception of Ononis 
biflora, where it is intermediate. The diameter of the hypocotyl is such as 
appears to be normally correlated with a high transition, except in Trigonella 
cretica, where it is unusually stout. It may be that the root-structure of the 
greater part of the hypocotyl isa character which, ensuring flexibility, is of 
LINN. JOURN.— BOTANY, VOI. XLI. G 
