LINNEAN SOCIETY OF LO>'J)OX. 25 



these specimens, Mliieh he placed in two genera, MeduUosa and 

 Cahimitea, have no analo<;ue among hving plants. 



His description of the genus j\IcdulJosa, which he founded, is on 

 tlie whole remarkably accurate, and some of his figures are 

 excellent and might still be used as adequate illustrations. Two 

 of his species, M. stellata and M. porosa, are the real stems ; 

 the third, M. elegans, consists of the leaf-stalks (afterwards 

 MiieloxDlon). It is odd that he should have placed these in the 

 right genus, for of course the structure is totally different frora 

 that of the stem. He no doubt mistook the hypodermal 

 strengthening zone of the petiole for the outer ring of wood 

 in the stem. 



In the description of the stem of M. stellata, he interpreted 

 the complex structure with surprising success, considering that 

 it is quite unlike anything in recent plants, consisting as it does 

 of a double system of peripheral and central steles, each growing 

 in thic]<ness by its own cambium. In fact he practically 

 recognised tlie " polystely " (to anticipate more than half a 

 century), for he describes the pith as containing many-rayed 

 stellate columns, constructed on the same plan as the radiating 

 outer zone, which he saw was itself a compound structure. He 

 points out that each radiating portion forms a whole by itself and 

 ])ossesses a special pith (einen besonderen Markkeru) (p. G5), 

 He rather spoils his excellent observations, however, by suggesting 

 that the internal stellate columns might be young plants which 

 grew up inside an old hollow stem ! 



His second genus of " Eadiati," Calamitea, may, he says, with 

 much probability be supposed to have a common origin with the 

 Calamites, so well known as impressions (p. 57). On this point 

 his knowledge was decidedly in advance of Brongniart's at the 

 same time. He arrived at this right conclusion by comparing 

 the striations of his petrified specimens with those on the casts 

 (p. 67). His Ccdamitea striata = Calamodendron striatum, Goep- 

 ])ert, and his Calamitea histriatu = Arthropitys histriata, Goeppert. 

 Thus he had already recognised the two chief groups of Calamarian 

 stems. 



Cotta's " Supplementary Eemarks " are partly on the subject 

 of the mode of preservation, but their chief object is to correlate 

 the impressions with the petrifactions, a laudable attempt in 

 which, with the one exception of the Calamites, he was singularly 

 unsuccessful. 



He was inclined to identify Trdncaulis with Lepidodendron, 

 some species of which (including the well-known L. obovatum) he 

 regarded as Ferns. He compares the ribbed Sigillarias with Cacti, 

 a view which, oddly enough, has re-appeared in the present day in 

 a work by the geologist Steinmann. At the same time Cotta iden- 

 tified these Sigillarian stems with his genus MeduUosa (p. 84). 



As regards the Calamites, which he rightly identified, he was 

 misled, like Brongniart in later days, by the internal structure, 

 though not to the same extent. He argues against their being 



