RACHIOPTEKIS CYLINDEICA. 59 



provisional conclusion that the bodies in question are really consti- 

 tuents, or derivatives, of the normal cell contents and not alien immi- 

 grants from without. On this view their mode of origin will have to 

 be sought in the changes brought about in the process of fossilisation, 

 but with regard to this I am not in a position to say anything. 



Finally, before leaving the subject, it may be worthy of notice that 

 the general occurrence and peculiarities of these bodies have made it 

 possible to use them to some extent as a diagnostic character of Rachi- 

 opteris cylindrica, and with such good results that determinations first 

 made by their aid have been subsequently confirmed by more rigorous 

 methods. 



Endodermis. 



At the innermost part of the cortex, where it abuts on the central 

 cylinder, one naturally expects to find an endodermis, and the sections 

 have been carefully scrutinised for indications of its presence. The 

 result is not so completely successful as could have been wished, since 

 it still leaves some doubt whether a specially differentiated endodermis 

 is or is not always present. The case appears to be somewhat similar 

 to that of Lycopodium clavatum, for we find here also thick-walled 

 elements abutting on the stele, and here a well-marked endodermis 

 cannot always be clearly recognised. But in favourable sections, e.g., 

 Nos. 104, 105 and 107, a layer of thin-walled elements is found on the 

 inside of the thick-walled inner parenchyma, which, in the shape of its 

 cells, their mode of union, and the appearance of the radial walls, bears 

 some resemblance to an endodermis (Fig. 1). Its cells are larger 

 than, and alternate with, those of the next layer on the cortical 

 side ; and they also alternate with those of the next layer within. 

 Hence it may be regarded as the innermost layer of the cortex, or the 

 phloeoterma of Strasburger. 1 



The Central Cylinder or Stele. 



If the layer of cells just referred to be really the phloeoterma, then 

 all the tissues within it must be those which constitute the stele. On 

 this view we can distinguish, more or less readily according to the state 

 of preservation of the specimens, (i.) a pericycle, (ii.) phloem, and (iii.) 

 xylem. 



^istologische Beitrage, III. 



