490 SECTIONAL TRANSACTIONS.—K. 
The object of the paper is to point out the probable connection between 
these variations, and to show how far they may be regarded as parallel series 
of specialisation. The possible correlation of external form with nuclear 
structure is discussed. 
Saturday, September 15. 
Excursions took place to (a) Ingleborough; (b) the Leet Valley, 
Flintshire. ws ; 
Monday, September 17. 
21. Dr. D. H. Scorr, F.R.S.—The Harly History of the Stele. 
The Lower Carboniferous flora is taken as a typical Paleozoic stage, from 
which to work back. The varied types of stelar structures then existing are 
briefly recalled, as represented among the Lycopods, Sphenophylls, Equisetales, 
Filicales, Pteridosperms and higher Gymnosperms. Our limited knowledge of 
the structure of Upper Devonian plants does not suggest that organisation was 
appreciably simpler at that period. 
In the Early Devonian the conditions were quite different. Though advanced 
types already existed (Palwopitys Muilleri), it is here that we first meet with 
really simple vascular plants (the Psilophytales). Of these, Asteroxylon was an 
undoubted Pteridophyte, comparable in its stele either with the Lycopodiacee or 
the Zygopterid ferns. In the Rhyniacee the slender centrarch or indeterminate 
stele reaches the limits of simplicity ; but were these plants Pteridophytes? 
Taking all the early types into consideration, there appears to be no ground 
for the assumption that the stele had a foliar origin. The independence of the 
stele is manifest throughout. It is only the more advanced forms of stele that 
are built ap of leaf-traces, and the extreme case of the Marattiacee appears 
to be exceptional and derivative. 
‘There is much reason to believe that a solid stele is primitive, so that the 
term ‘protostele’ appears justified. On the other hand, there are no sufficient 
grounds for the hypothesis that the typical root-structure was primitive for 
the stem also. In particular lines such a stage may have been passed through, 
but this was not the case generally. 
22. Prof. W. H. Lana, F.R.S.—The Organisation of the Plant in 
the Vascular Cryptogams in the Light of Fossil History and 
Causal Morphology. 
The main morphological problems in the organisation of land-plants can be 
studied in the Vascular Cryptogams, which not only have a long geological 
history, but are suitable for experimental work. The problem of the segmenta- 
tion of the shoot composed of stem and leaves was very early stated on formal 
lines. Comparison of existing plants, and even those of the Lower Car- 
boniferous Period, does not provide evidence to decide between alternative 
views. Putting questions of relationship aside, it seems possible to obtain 
further evidence along both historical and experimental lines. On the historical 
side the plants of the Early Devonian Period are especially interesting in 
this respect, since they may afford examples of nascent shoots. Normal develop- 
ment, and especially some deviations from it, are instructive and open to 
physiological study. It is only possible to mention the further problems 
presented by the root and the spore-bearing organs of the Vascular Cryptogams, 
but that of the organisation of the shoot illustrates the limitations and the 
hopefulness of work both on historical and causal lines. Any definite con- 
clusion would be premature, but on the whole the increase of knowledge appears 
to be in favour of some segmental or phytonic construction of the shoot. In 
the present state of morphology the usefulness of comprehensive theories, 
whether evolutionary or physiological, seems doubtful. 
23. Prof. J. McLean THompson.—Developmental Morphology and 
its Bearing on Systematic Physiology. 
An attempt is made to trace by developmental methods a phyletic tendency 
in a group of Angiosperms from its initiation. In particular, progressive sterility 
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