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SECTIONAL TRANSACTIONS.—K. 447 
in recent years. The peculiarities long known to exist, for example, in the 
embryos of the higher vertebrates are interpreted either as direct adaptations 
to embryonal environment or as representing merely larval phases which are of 
no real evolutionary significance. Recent studies carried on in the author’s 
laboratories on the anatomy of Mesozoic conifers throw an interesting light on 
the situation. It cannot be claimed that the seedlings of the higher seed-plants, 
in particular the seedlings of the living conifers and dicotyledons, are in any 
sense larval in the signification of the term used on the zoclogical side. In the 
case of the conifers we are now in a position to compare the details of structure 
in the seedling of living fofms with the mature organisation of their Mesozoic 
ancestors. By such comparison it is found that both in the Araucarian and 
Abietinean conifers, which at the present time are in competition for the place 
of the most primitive conifers, the seedlings of living forms supply an exact 
recapitulation of the organisation of these types in the Mesozoic. No more 
striking inductive evidence could be supplied for the truth of the doctrine of 
recapitulation, since inductive logic furnishes the basis of scientific reasoning. 
A further interesting corollary of the doctrine of recapitulation, when studied 
in the light of the comparison of living with fossil forms, is that the root and 
reproductive axis also perpetuate ancestral conditions, and that these may also 
frequently be recalled by experimental means. ‘The importance of this situation 
from the general biologiéal standpoint is not open to question. 
12, Dr. Eruen N. Mines THomas.—The Primary Vascular System in 
Phanerogams: its Characters and Significance. 
The results obtained in the investigations of the last twenty years on ‘ Seedling 
Anatomy ’ have been held to be conflicting and disappointing. This is largely due 
to false comparisons having been made as to fact and theory. 
Seedling Anatomy considered as a branch of Comparative Anatomy probably 
furnishes more comparative data than any other part of the plant body and shows 
features of surprising constancy and widespread occurrence. 
It is possible to make the following generalisations, founded on the comparison 
of more than 1,000 species. 
In the great majority of species :— 
1. The first formed primary strands of xylom and phloem are developed on 
separate radii in hypocotyl, root and cotyledon, so that they conform, throughout 
the plant body, to the alternate or radial rather than to the collateral arrangement. 
In this respect, at any rate, there is therefore no sharp distinction between the root 
and shoot anatomy in the earliest vascular system O X O (see Chauveaud, Thomas). 
The apparent exceptions are yielding to further investigations—Ricinus (Thomas, 
Journal of Linn. Soc., 1922; Sapotacee, Thomas, Brit. Ass. Rep., 1923 ; Monocoty- 
ledons, Chauveaud, 1921, Thomas, 1924). 
2. The primary radial arrangement is obscured and even obliterated in most 
species by the disappearance of the alternate xylem at a very early age (one cause 
of false comparisons) and the production of collateral primary and secondary xylem, 
so that what may be regarded as a single vascular unit (double bundle or triad, Thomas, 
1914) in the primary condition, appears as two units at a slightly later age. 
O O (Cf. Scott, Struc. Bot., Vol. I.) 
X X (7th with later Eds.) 
In the view of the writer this phenomenon undoubtedly accounts in most cases even 
for the two separate strands met with in the cotyledon of certain Monocotyledons 
(e.g. Cordyline) (Chauveaud). 
Single (‘ double ’) strands are found in the monocdtylous Dicotyledons Ranunculus 
Ficaria, Anemone apennina, Conopodium denudatum, Cyclamen persicum, and this 
fact strengthens the above interpretation of the vascular strands of the cotyledon of 
true Monocotyledons. 
Almost without exception in dicotyledonous forms and in a number of monocoty- 
ledons and pseudo-monocotyledons examined by the writer :— 
3. The plane passing through two of the poles of the primary root passes also 
through the centre of the two cotyledons or one cotyledon (Cruciform type of Thomas). 
In the diarch forms it is these poles alone which are developed. In the monocotylous 
Dicotyledon Conopodiwm denudatum, however, the diarch plate is at right angles to 
