144 The “ Origin of Gym nosperms ” 
strobns. You could not quite run Cheirostrobus and the Lycopods 
together. Cheirostrobus was a representative of an enormously 
ancient synthetic group, and to derive the Araucarieae from that was 
a very different thing to deriving them from ordinary commonplace 
Lycopods. Professor Oliver in a recent remarkable course of 
lectures had referred to the possible existence of a very ancient 
common group from which all the lines of Pteridophytic descent 
might have sprung, and had suggested that while the Spheno- 
phyllineae had retained the fertile ventral lobe of the sporophyll, 
this character might have spread down the Filicinean line of 
descent and reappeared in the Gymnosperms. This was a hold 
hypothesis, but it was a very different thing to deriving Conifers 
from Lycopods. The gap between the Araucarieae and the Lycopods 
was much wider than any gap we should meet if we took the 
Filicinean view of Coniferous descent. If he had had unlimited time, 
he would have liked to have made some concessions to Mr. Seward. 
He would have liked to point out that he could have supplied 
9.0 Mr. Seward with better ammunition than he had used. 
There were some striking anatomical peculiarities, such as 
the double leaf-trace in Sigillariopsis, the tracheal elements in 
the medullary, rays and the transfusion-tissue in the leaves of both 
Lycopods and Conifers which undoubtedly supplied points of 
resemblance between the two groups. The transfusion-tissue might 
find its explanation in homology with part of the primary wood of 
Pteridosperms, and the other instances were probably cases of what 
Professor Lankester had called homoplastic development, especially 
as they appeared in the higher rather than in the lower groups of 
Conifers. 
After some remarks from the President, Mr. Robert Boyd 
Thomson (Toronto), rising at 9.7 at the invitation of the President, 
said that he did not want to join in the discussion, but he hoped to 
add some difficulties to it. He had been studying the coat of the 
megaspore (embryo-sac) in Gymnosperms, and his attention had 
been specially called to the Araucarieae. He thought that on the 
assumption that the Gymnosperms were monophyletic, the thicker 
the spore-coat the more primitive the group. He found that the 
coat was very uniform in structure throughout the different groups, 
consisting of an outer suberised layer, the exosporium, and an inner, 
incompletely suberised layer, the endosporium. Cycads had the 
thickest coat and Ginkgo came next. Conifers had a coat very 
variable in thickness ; it might be quite thin or even absent, while in 
Gnetales the coat was very thin. Of the Conifers the Abietineae 
had a uniformly thick coat which thinned out at the apex. In the 
Cupresseae the coat was much thinner, which seemed to correspond 
with the specialisation of the group. The Taxeae had no coat 
whatever. In Podocarpeae, Podocarpus had none, while that of 
Dacrydium was quite thick. The Araucarieae had quite a different 
type from the rest of the Conifers. The coat was single, the 
exosporium having disappeared. The endosperm was “ rumi- 
9.15 nated ” and in correspondence with this folding in and out the 
megaspore had lost its exosporium, just as in the case of the 
pollen tube which had also to burrow between the cells of the 
ovule. The megaspore in fact could not be distinguished from the 
pollen tube, especially when both were in a multinucleate condition. 
So that the Araucarieae were quite isolated in this character. In 
the vegetative structure there was a resemblance to Cordaiteae, 
