OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
209 
]ysigenetic hypothesis is strong and definite. We never find that the tracheids 
forming the inner border of the ring 6, in specimens like figs. 10-13. have their avails 
torn or disorganised, which must have been the case had these inner tracheids been 
subject to a continuous destructive action. 
Professor Hugo ue Vries, of Amsterdam, who at my request has given some little 
attention to this subject, has suggested to me the question—Are such sections as I 
have represented in figs. 7-15 really examples of branches of the same plant in various 
stages of development ? About this I have no doubt whatever. The twig in these 
arborescent exogenous Lycopods, as in modern exogenous trees, is but the young state 
or precursor of the future branch. It is a material point, bearing upon this part of 
the subject, that the above arguments are not based upon some isolated example of 
these Lepidodendroid plants. My specimens show that the conditions to which I am 
once more calling attention are not isolated or rare. They are characteristic of the 
entire Lepidodendroid family, ivhether arhorescent or otherwise. Throughout the 
entire group we know that the large dichotomous branches did not shoot into existence 
as such. They were all once slender twigs, and I am convinced that such series of 
sections as abound in my cabinet, corresponding to those now represented in my 
figures 7-15, are illustrations of twigs and branches of the same plant in successive 
stages of their growth. 
I should also like to remark on the objection that in this and some of the preceding 
Memoirs I am in danger of establishing new species without sufficiently defining 
them. In fact, the establishment of species of Coal-plants in the strict sense of the 
word has not been my object. The difficulties in the way of doing this are, in my 
judgment, insuperable. In the earlier of this series of Memoirs I made no attempt to 
attach specific names to the objects which I described. I mainly sought to throw new 
light upon the morphology and histology of the Carboniferous plants. I soon found 
that, whilst one type of structure was common to the entire group of Lepidodendroid 
and Sigillarian plants, this type was subject to numerous remarkable modifications as 
regarded the details alike of structure and of growth. It became necessary, by some 
symbol, to facilitate reference to each of these modifications. There was no room for 
doubting that where such details were conspicuously different I was dealing with 
forms that were specifically distinct. But the conv^erse was not necessarily true. It 
was quite possible, though incapable of demonstration, that identical modifications of 
vegetative structures might exist in plants in which the reproductive organs might 
have shown specific distinctions, as is so commonly the case amongst living Lycopodia 
and Selaginellse. Brongniart, however, had already followed the example set by 
WiTHAM of employing the Linnean binomial nomenclature under similar circumstances, 
in his descriptions of Lepidodendron Harcourtii, of Siyillaria eleyans, and of Sigillaria 
spinulosa ; and after some consideration I deemed it best to follow so distinguished a 
precedent. At the same time, I wish it to be distinctly understood that my specific 
names are intended to repiesent modifications of types of organisation rather than 
specific forms.— The Botanical Laboratories, Owens College, Jidy 31, 1889. 
MDGCCLXXXIX.- B. 2 E 
