The Meeting of the British Association at York. 183 
the vascular structure of the seedlings of several species belonging 
to the Amarantaceas, Aizoaceae, Caryopbyllaceae, Portulacaceze and 
Chenopodiaceae were recorded and the same type of structure found 
in all, with the exception of Allionia. in which somewhat more 
complicated phenomena are met with. 
Mr. A. G. Tansley communicated some of the results obtained 
by Miss E. N. Thomas and himself in the course of an extended 
investigation into the vascular structure of dicotyledonous and 
gymnospermous hypocotyls. It was pointed out that whether or no 
the cotyledons are the equivalents of the first leaves of Pteridophytes 
and the hypocotyl of the first-formed stem, in any case these are 
well-marked organs in the seed-plants and the legitimate subject of 
comparative investigation. The different types of “transition” 
between the collateral structure of the cotyledonary vascular tissue 
and the radial structure of the primary root-cylinder are found, 
with a very few exceptions, to be modifications of one great plan, 
while the exceptions that are known may very possibly be traced 
back to the same place though recorded cases are at present too 
isolated for comparative treament. The most widely spread type is 
found to be characteristic of various families of dicotyledons and 
also among Conifers. Among Cycads and Araucarieae a more 
complex type prevails, with a larger number of cotyledonary traces 
and the evidence leads to the conclusion that the simpler type is 
derived by reduction through various transitions from the more 
complex. There is a particularly clear series of this kind demon¬ 
strable among the Gym nosperms. The evidence from the more 
primitive dicotyledons is not at present so unmistakable. Some 
possible factors that might have brought about the suggested 
changes were indicated, and stress was laid on the tentative nature 
of some of the conclusions. 
Dr. Scott remarked that among the Filicinean, Pteridospermic 
and Gymnospermic series there was much general evidence of the 
primitiveness of megaphylly. Among the Equisetales, Archaeo- 
calamites and the Devonian Pseudobornias indicated the same 
conclusion. Only in the Lycopodsdid we find, apparently, primitive 
microphylly. Reduction seemed to be an extremely common 
phenomenon in the evolution of the vascular plants. There was a 
presumption in favour of the cotyledons of Spermophyta being 
leaves because of the transition, shown by the absence of a resting 
stage in early Cycad ontogeny, between the Pteridophytic and the 
Spermophytic types. Unless the cotyledons were leaves this embryo- 
