SEEDLING STRUCTURE IN THE LEGUMINOS Ж, 101 
The answer to this question can only be given after certain other problems 
have been considered, the most important of which is the relation of 
plumular traces to the vascular structure of the hypocotyl. 
PLUMULAR TRACES IN HypocotyL AND Коот. 
In the vast majority of epigeal seedlings it is found that the primary 
vascular system of the cotyledons, hypocotyl, and root is complete in itself ; 
all the protoxylem strands contained in the root pass up into the cotyledons *, 
and a primary or, as it has been called, foetal or larval circulation is 
established in the seedling without reference to subsequent plumular 
developments, When the plumule develops in such cases (and there is 
frequently a marked pause between the unfolding of the seed-leaves and the 
first foliage leaf, when compared with the ordinary succession of foliage- 
leaves), its vaseular system is simply superposed upon that of the typical 
morphological constituents of the seedling. In most epigeal types the 
hypocotyl has lost the capacity for forming primary xylem before the 
plumule begins activity ; and therefore the plumular traces are represented 
in the hypocotyl by secondary xylem only. 
In a considerable number of large epigeal seedlings, however, the plumule 
begins to grow before the hypocotyl has completed its phase of elongation ; 
and in such cases tracts of primary xylem are differentiated from the 
desmogen strands common to plumule and hypocotyl ; in fact the plumular 
traces are represented in the hypocotyl by primary xylem. Such primary 
xylem, however, usually stops short in the hypocotyl and is not prolonged 
into the root. This type of connection is found, for instance, in many 
Phaseoleze. 
In other cases, particularly when germination is hypogeal, the plumule 
has already attained a considerable size while in the embryo; and on 
germination its development is rapid. The hypocotyl remains short, and 
primary xylem is developed in continuous strands between the root 
and epicotyl. The degree to which this connection is made varies in 
different cases, often simply as the result of the varying precocity of 
plumular development. А series of cases is here given, illustrating the 
warious degrees of connection between epicotyledonary and hypocotyle- 
4donary axes. 
(a) Plumular traces represented in hypocotyl and root by secondary 
xylem only. (Most small epigeal seedlings). 
(b) Plumular traces represented in the hypocotyl by primary, in the 
the root by secondary, xylem. (Phaseolez spp.) 
* Unless, of course, some of them disappear on the way. 
