472 
Holden and Daniels. — Observations on the 
of the smaller cotyledon to form a large mass (Fig. 50). Only a single root 
is produced at the point normally occupied by the root-whorl, and this is 
continuous with the pole which forms the midrib of the larger cotyledon 
(Figs. 51, 52). The tap-root is tetrarch. It is obvious that the reduction in 
the size of the cotyledon exercises an appreciable effect on the vascular 
symmetry even at the base of the hypocotyl. and the seedling suggests 
comparison with Abronia umbellata and A. vitlosa, in which a difference in 
the size of the cotyledons is a normal feature. Hill and de Fraine ( 17 ), 
who have investigated the seedling anatomy of these two species, show that 
here also the vascular strands of the reduced cotyledon play a smaller part 
in the transition phenomena than those of the larger one, though the details 
of transition differ widely from those of Impatiens Roylei. The second 
specimen is remarkable in that it combines inequality in the size of the 
cotyledons with syncotyly, this being unilateral as regards the laminae but 
involving both petiole margins (Fig. 7). The bundle system of the smaller 
cotyledon consists of a series of collateral strands, one of which occupies the 
position of the midrib (Fig. 53). At the apex of the hypocotyl these 
bundles have been reduced to two laterally situated pairs, a phloem group 
marking the site occupied by the ‘ double ? bundle in the normal cotyledon 
(Fig. 54). Of these, one pair, after the union of its constituent bundles, 
fuses with the adjacent lateral from the larger cotyledon, the vascular system 
of which is normal (Fig. 55). The strands of the other pair, after union, form 
an endarch xylem group which remains independent of the adjacent lateral 
and forms a pole. The lateral thus left continues down the hypocotyl for 
some distance (Fig. 56), but ultimately dies out, so that the hypocotyl 
develops a triarch symmetry and produces three lateral roots at its base 
(Fig- 57 )* Subsequently a fourth pole is developed by the tap-root in the 
plane corresponding to that passing through the independent lateral to 
which reference has just been made. The behaviour of the strands in the 
second seedling recalls that described for a somewhat similar case by one of 
us ( 18 ), in which a seedling with unequal cotyledons developed an asym- 
metrical triarchy in the hypocotyl owing to the absence of a £ double ' 
bundle midrib in a smaller cotyledon. It is difficult to say whether the re- 
placing of the normal median symmetry by a lateral bundle concentration is 
to be correlated with the reduction of the cotyledon or not, but this is doubtful. 
The available material is quite inadequate for the determination of the 
homologies of the bundles involved, but it is worthy of note that Davey ( 9 ), 
in her description of the seedling anatomy of certain Amentiferae (e.g. Jug- 
lans cinerea , Pterocarya rhoifolia ). records a loss in the relative importance 
of the median cotyledonary strand and a corresponding increase in the 
transition value of the laterals, though the similarity between these forms 
and Impatiens is not a close one. 
The formation of a very short cotyledonary tube at the base of the 
