80 MR. R. H. COMPTON : AN INVESTIGATION OF THE 
forming a median collateral bundle (е. g. Lupinus mutabilis). In a few cases, 
however, the transition is incomplete below the node (e. g. Genista 
ethnensis). 
The level of the transition varies from low in the stoutest seedlings 
(Lupinus spp.) to high in the slenderest (Genista «wthnensis). The seedlings 
of intermediate diameter have rather diverse levels of transition relatively 
to collet and cotyledons. A more strict accordance is produced if we take 
into account the length of the hypocotyl as well as its diameter; it is 
found that the order of transition level from low to high is also the order 
of bulk of the hypocotyl, from great to small. This seems to imply that the 
apparent level of transition depends partly on the absolute distance between 
collet and cotyledons. Given two seedlings of equal diameter: if the 
velocity of transition be the same in both, the level will appear to be lower in 
the one with the longer hypocotyl; we may thus compare Crotalaria striata 
with Cytisus canariensis. It is possible that in some cases the absence of 
fibres may necessitate greater mechanical strength on the part of the aerial 
hypocotyl, and may thus produce a lower transition than would be the case if 
fibres were present (compare Laburnum vulgare with Spartium junceum, for 
instance). The height to which the cotyledons are borne above ground may 
also have an influence (е. g. Ulex europeus). 
Owing to the uniformity of structure the Genistee are a favourable. 
tribe for the study of the factors which influence the level of transition. 
It appears that this uniformity must be due to a hereditary factor, and 
that therefore seedling characters may to some extent be useful as indications 
of relationships. This view is strengthened by the fact that in Ononis, 
one of the Trifoliese, but nearly related to the Genistes, a Genistew-ty pe of 
structure may occur. 
TRIFOLIES. 
The great majority of the Trifoliew are of herbaceous habit, whether 
annual or with a perennating root-stock: rarely the habit is shrubby 
(Ononis rotundifolia). Many of the species are weak-stemmed and 
procumbent. 
The seedlings are all epigeal, so far as is known, and in most cases the 
cotyledons are borne high above the ground. The hypocotyl is slender 
and rather weak. The cotyledons are leaf-like, more or less ovate, often 
shortly petioled ; in the genera Trifolium, Melilotus, Trigonella, &c. there 
is a joint between the lamina and the petiole similar to that seen in the 
foliage-leaves : its presence may be an example of correlative variation 
between cotyledons and leaves if taken as indicating a derivation of the latter 
from a higher degree of pinnation (cf. Berberis, Citrus); or it may be 
regarded simply in the light of its function as a hinge for nyctitropic 
movements. This joint is absent from the cotyledons of Medicago spp. 
