Sept. at, 1871] 

classification, elevate the vegetative organs at the cost of 
the reproductive ones. I reply Iam merely applying prin- 
ciples already adopted by botanists throughout the world. 
They are those of DeCandolle, of Endlicher, of Lindley, 
of Brongniart, and of Balfour. These writers, in common 
with most others, recognise primary distinctions that are 
purely vegetative. Not only are those which separate 
vascular from cellular plants of this character, but the 
further ones of exogens, endogens, acrogens, and thallo- 
gens are of the same nature. The fact of the closest 
resemblance of the inflorescence, and of the formation of 
the embryo in the embryo-sac in the two groups, does not 
prevent the separation of the flowering plants into exogens 
and endogens. Turning from the phanerogamous to the 
cryptogamic plants, we find that nearly every writer of 
importance adopts vegetative features as the basis of his 
classification. DeCandolle divides his Acrogevs into those 
which have and those which have not vascular tissues. 
Endlicher’s primary term Cormaphyta refers to a vegetative 
feature, viz., the possession of a stem, whilst his secondary 
divisions of Acrobrya, Amphibrya, and Acramphibrya all 
refer to the mode of growth and not to fructification. 
Lindley again distinguishes his flowerless plants according 
as they are acrogens or thallogens ; whilst Balfour cha- 
racterises them primarily as acrogens or cormogens and 
thallogens. In thus dwelling upon the vegetative element 
of the cryptogams, I am merely treading in the steps of 
nearly every writer of note who has written on these sub- 
jects. So much, therefore, for the primary point. 
In many of the discussions which have taken place, my 
opponents have made the mistake of supposing that I was 
trying to prove these fossil coal-plants to be dicotyledonous 
exogens. Whereas what I have throughout contended for 
is that they are true cryptogams with an exogenous woody 
axis. Mr. Carruthers says, “‘ The plants were true cryp- 
togams, and in their organisation agree in every essential 
point with the stems of Lycopodiaceze” (NATURE, p. 337)- 
With this I of course agree, but I contend that we must 
interpret the lower forms by the higher and not the higher 
by the lower. In Carboniferous ages, these plants became 
superb forest trees, and consequently their stems attained 
their full development, growing year after year, from their 
almost microscopic condition when they burst from a mi- 
croscopic spore, until they became stately trees, such as 
were revealed at Dixon Fold, and such as are illustrated 
by specimens now in the Manchester Museum. In the 
course of their magnificent development the stems were 
-gradually fitted to sustain an enormous weight of branch 
and foliage. This was done by the development, within 
those stems, of a vascular woody cylinder, which grew 
thicker year by year; such thickening being the result of 
additions to the exterior of the previous growths. We here 
come to a definite issue. Do my opponents intend to 
deny the existence, in these arborescent carboniferous 
plants, of these thick ligneous cylinders, or to dispute that 
they grew in the way described? I think they cannot 
possibly contemplate doing so. Dr. M‘Nab says botanists 
are agreed in this, that “ Lepidodendra and their allies 
are closely related to other Lycopods. Now we know 
that the Lycopods, /ke the Ferns, have closed fibro- 
vascular bundles; bundles which can only grow fora 
certain time, and then, all the cambium being converted 
into permanent tissue, growth must cease.” The italics 
in the preceding paragraph are my own, With the above 
remark, so far as Ferns are concerned, I thoroughly agree. 
The facts so correctly stated by Dr. M‘Nab constitute 
one of the fundamental bases of my proposed classifica- 
tion. The vascular bundles ave closed in all the small 
ferns, and they remain equally so in the Cyatheas and 
other arborescent ferns which attain to stately dimensions. 
The development of this type into a lofty tree has not 
materially modified the structure of the stem which recurs 
in the most dwarfed species. But when Dr. M‘Nab 
applies the above general statement to the Lycopods, 
NATURE 


409 

facts do not sustain him. The huge lepidodendroid car- 
boniferous plants give it a direct contradiction. They 
have zof closed vascular bundles, and their growth did 
not cease after a-limited time, but was obviously con- 
tinued, being sustained by a cambium layer, until the 
plants assumed the magnificent dimensions which their 
fossil remains now exhibit. That the large vascular 
cylinder of the fossil forms is a development of what is 
seen, not only in Lycopodium chamecyparinus referred 
to by Dr. M‘Nab, but in every one of the numerous 
Lycopods of which I have examined sections, I have never 
denied. Quite the contrary. But I repeat we must inter- 
pret the significance of the /east developed form by that 
which is most developed. Consequently we must regard 
the irregular vascular bundles which exist, commingled 
with cellular tissues, in the axis of each living Lycopod, 
as a degraded wood cylinder, whose nature can only be 
understood by reference to what it once was when its 
parent tree was one of the glories of the primeval forest. 
The race as a whole has become degenerate, and the stem 
being no longer called upon to sustain a lofty superstruc- 
ture, its structure has become equally degenerate. 
I will not enter in detail into the question of the nomen- 
clature of the various parts of these exogenous crypto- 
gamic stems, but reserve that subject for some other 
occasion, after my detailed memoirs now in the hands 
of the Royal Society have been published. 1 will merely 
express my conviction that Mr. Carruthers, who differs 
widely from me on the subject, assumes the very question 
in debate between us. 
He holds that we can draw no parallel between the con- 
ditions existing in the stems of Cryptogams and those of 
Phanerogams. This is precisely what I contend we can 
do, and I trust to be able, as my self-appointed task pro- 
ceeds to its conclusion, to demonstrate to the botanical 
world that I have abundant reason for so doing. This is 
a question wholly resting upon facts, and until those facts 
are fairly before the world,I object to the adoption of any 
a priori conclus?n on the subject. Consistently with his 
views Mr. Carruthers objects to my applying to the stems in 
question such terms as medulla and medullary rays ; especi- 
ally objecting to the application of the term medulla to a 
structure containing vessels, z.¢., a vascular medulla ; but 
Nepenthes has a vascular medulla, as well as some other 
phanerogamous plants, and no one presumes to deny the 
medullary character of such a tissue, because it happens 
to have vessels in it. The medullary character of the 
structure does not rest upon the basis of its being wholly 
devoid of vessels, neither does their occasional presence 
militate against its being a medulla. 
In the preceding remarks I have confined myself sub- 
stantially to the task of making clear the points at issue 
between my opponents and myself. In adopting my 
views of the exogenous structure of the stems in question, 
I am but following in the steps of some of the ablest of 
living botanists. M. Adolphe Brongniart, than whom no 
higher authority can be named, not only adopts the 
exogenous theory, but is so deeply impressed with its force 
that he denies the probability of many of the plants in 
question having been cryptogamic. He places them 
amongst the gymnospermous exogens. Recent events, 
however, have shown that though exogenous they are true 
cryptogams. How absurd, then, to apply to such stems 
the term acrogen or acrobrya! This controversy must 
be ultimately settled by the logic of facts, not by vague 
opinions, and to these I confidently appeal. The details 
of my proposed classification can only be discussed when 
all the facts are before the public. When this is the case, 
I hope to show that my proposition not only does no 
violence to the true affinities of living cryptogams, but that, 
in bringing the ancient and modern types into a philoso- 
phical relationship, it accomplishes what, under existing 
systems of classification, it is impossible ta do, 
W. C, WILLIAMSON 
