HICK : OUR KNOWLEDGE OF THE YORKSHIRE CALAMITY. 
3 
rootlets on a root is known to occur. On Stigmaria the rootlets 
have such an arrangement, but by many authorities it is maintained 
that Stigmaria is not morphologically a root. 
It will be noted moreover that nothing is said of the structure 
of the organs called roots and rootlets, and so far as I can gather our 
knowledge on this point is a perfect blank. It is true that Renault" 
would have us believe that all the forms of Astromyelon are roots of 
Calamodendron and Artkropitys, Astromyelon dadoxylinum being 
the root of the former, and Astromyelon Augustodunense that of the 
latter. But in the Yorkshire forms of Astromyelon there is nothing 
characterestic of root structure, and we may therefore venture to 
reject this determination, as is done by Solms-Laubach, until it is 
supported by better evidence than it is at present. 
The Stem. 
From the accounts given in the literature, ably summarised by 
Solms-Laubach,t it would seem, as already stated, that some species 
of Calamites possessed subterranean rhizomes w T hich gave off two 
kinds of branches. The first of these remained beneath the ground, 
like the parent rhizome, to whose nodes they were attached by a 
broad base. The second were aerial shoots, which were inserted upon 
the rhizome like the preceding, but their bases were curved and 
narrowed into a conical form, and had a relatively large number of 
short internodes. It would seem, too, that these aerial shoots bore 
latemal branches, which were cylindrical and of the non-tapering 
kind. The aerial stems arising from the rhizome were frequently 
tufted, forming a group round a common centre, whence it has been 
concluded they were annual, like those of the gigantic Equisetums of 
the Trias. 
The laws of branching of the aerial shoots have been at least 
partially worked out by Weiss,J who includes the number and 
arrangement of the branches among the characteristics of the four 
groups into which he divides the Calamitw. 
* Nouvelles recherches sur le genre Astromyelon. Memoires de la Soc. des 
Sciences Naturelles de Saone et Loire, 1885. 
f Fossil Botany. Eng. Ed., pp. 308, 309. 
X Beitrage zur fossilen Flora III., Steinkohlen-Calamarien II. 
