336 Proceedings of the Royal Society of Edinburgh. [Sess. 
G Wynne- Vaughan approached this naturally through those types with a 
tubular stele in the axis, which he designated “ solenostelic,” reviving a 
term already introduced by Van Tieghem. A careful analysis of the 
anatomy of Loxsoma, as a typical example of this structure, was followed 
by comparisons with numerous other genera, such as Hypolepis, Denn- 
stcedtia and Pteris. The gradual steps to dictyostely were thus traced, 
and the demonstration given that not only by comparison, but also in the 
individual life (e.g. Alsophila), the transition depends upon the overlapping 
of the foliar gaps in an abbreviated axis. The facts were embodied in two 
papers, entitled “ Observations on the Anatomy of Solenostelic Ferns,” 
published in the Annals of Botany , 1901, 1903. These contain a great 
body of condensed comparative observation, showing that solenostely and 
dictyostely are related conditions. The origin of medullary vascular tracts 
within the solenostele was also traced from their simplest beginnings. 
But still there remained the more difficult question how the solenostelic 
state itself was related to the protostelic. Towards the solution of this 
problem resort was made to comparison of certain fossils related to the 
living Osmundace93. The work was carried out in happy co-operation 
with Dr Robert Kidston, F.R.S., of Stirling. This co-operation was real 
and equivalent. The one partner brought to bear on the problem a wide 
knowledge of fossils from the stratigraphical point of view : and he had 
already taken up a cognate inquiry in the Sigillarias. The other supplied 
critical and expert anatomical experience based upon the study of living 
plants. The result is a series of beautifully illustrated Memoirs published 
by the Royal Society of Edinburgh (“ On the Fossil Osmundacese,” Trans. 
Roy. Soc. Edin ., 1907, 1908, 1909, 1910, 1914). The fossil material was of 
world- wide origin, but chiefly from New Zealand and from Russia. In a 
sequence of plants, dating from the Permian Period to the present day, and 
shown to be really related to one another by many structural similarities, 
an anatomical progression was traced which follows most convincingly the 
successive stratigraphical horizons. It illustrates steps in the medullation 
of the stele and in the amplification of the leaf -trace, and it throws light 
upon the probable origin of the leaf-gap. Some still hesitate in full 
acceptance of the far-reaching conclusions which were drawn : but in most 
quarters the Memoirs of this magnificent Series are held as botanical 
classics; and none can be blind to the validity of the methods, or the 
acuteness of the internal criticism which they show. Though the details 
of the progression from the protostele to the confirmed solenostele are 
not fully demonstrated in them, the foundations are securely laid, and 
others are already building upon them. 
