RELATIONS OV CALAMODKNDRON TO CALAMITES. 257 



rayons medullaireSj du centre k la circonference "^. 

 The above description agrees with sections in my 

 cabinet, for which I am indebted to Professor Edouard, 

 Graf von Solms^ of Gottingen, with the exception of the 

 continuity of the central medullary ray last referred to. I 

 find that this ray is not regularly continuous, but 

 decidedly irregular and interrupted in its continuity : 

 indeed tangential sections of these fibrous zones exhibit 

 rather numerous narrow, vertically elongated^ lenticular, 

 medullary rays, composed of one, two, or three vertical 

 rows of cells; those rays nearest the centre are un- 

 doubtedly the largest and most conspicuous, but they are 

 not continuous, merely primi inter pares. 



Had the above description stood alone, no confusion 

 would have resulted ; but on p. 48 of his Tableau, 

 M. Brongniart makes the following observations : — 



" Je serais done porte a penser, qu^on a confondu sous 

 le nom des Calamites deux groupes des vegetaux tr^s 

 diff(^rents. L^un, comprenant les Calamites h ecorce 

 mince, reguliere, recouvrant le noyau central d^une couche 

 charbonneuse qui en suit tons les contours, qui montre a 

 sa surface externe des stries et des articulations tres nettes 

 des insertions de rameaux appliques sur des articulations 

 depourvues de gaines ou en oflrant quelquefois une etalee. 

 Leur structure est celle que je viens de decrire. 



L^autre, comprenant les Calamites k ecorce charbonneuse, 

 epaisse, qui, exterieurement, ofire h peine des traces de 

 stries lougitudinales et d^ articulations, dont le noyau 

 interne correspondant h la tige est, an contraire, profonde- 

 ment sillonne et presente des articulations tres marques. 

 Ces tiges, lorsque leur partie centrale a conserve sa struc- 

 ture, paraissent ofi'rir celle decrite par MM. Cotta, Petz- 

 holdt et Unger dans les Calamitea, c^est-a-dire une moelle 



* Loc. cit. p. 50. 

 SER. III. VOL. X. S 



