470 Holden and Daniels . — Observations on the 
contact between the two types of seedling have been established in four 
respects, namely : 
1. The proof that the coalescence of midribs is possible. 
2. The proof that a coalescence of cotyledonary axillary buds is 
possible. 
3. The fact that hypocotyl and root show similar types of vascular 
modification. 
4. The fact that the modifications in the epicotyl are identical. 
Quite apart from their significance as links between the two types of 
seedling, the vascular modifications have an additional interest as illustrating 
how such seedlings, whilst retaining certain ancestral features, may modify 
these and add to them. Syncotyly has inevitably brought with it a suppres- 
sion of certain of the vascular strands, and it would seem that this modifica- 
tion of the normal symmetry has evoked a response in many cases 
consisting of either the modification in relative importance of the persistent 
lateral vascular components or the introduction of entirely new strands into 
the hypocotyl and root. It seems impossible to assign any phyletic signifi- 
cance to these modifications, and one is compelled to assume that the 
impetus to change is physiological. If we make that assumption we are 
confronted with the difficulty that seedlings below the average in size may 
show a new complexity far in advance of that shown by seedlings above the 
average size which have retained the simplified vascular features imposed 
upon them as a result of compression. It is' possible that accurate measure- 
ments of the total bulk of the vascular system and of the transpiring and 
assimilatory areas would show that there is a definite relationship between 
these, but the whole problem only serves to stress our profound ignorance 
of many of the fundamental features of seedling physiology. 
The literature of seedling anatomy contains a number of references to 
an increase in the number of root-poles from above downwards, and in some 
of these a physiological explanation of the phenomenon is suggested. 
Thus Sargant ( 26 ), speaking of the development of new poles in Fritillaria 
alpina and F. imperialism regards this as ‘ due to the persistence of the 
primary root and its physiological activity, which renders a considerable 
girth necessary 5 ; whilst Hill and de Fraine ( 16 ), referring to a similar 
phenomenon in the Cycadaceae, believe that the probable cause is ‘ that the 
swollen axis requires a greater dispersal of the vascular tissues’. There is, 
however, no obvious reason to account for the increase in the number of 
root-poles in cases such as that of Opuntia Tuna , Series B, described by 
de Fraine (10). While the general trend of the present investigation has 
been to show that the two types of seedling have a syncotylous origin, 
a careful search has been made for seedlings showing marked inequality of 
the cotyledons, and of these two have been obtained, one of which is 
syncotylous in addition. Neither shows any affinity with the seedlings 
