TJic Fossil Plants of the Coal Measures. 107 



the adenoid organ. In addition to its ordinary tissues in 

 the interior of the leaf, the leaf-trace is large and further 

 surrounded by a number of large, but very short, almost 

 spiral tracheae, intermingled with the leaf-parenchyma. 

 The various tracheae of this plant, when well preserved, 

 exhibit a feature long found, onl}' in a very rare form, from 

 Yorkshire (L. mundum). But I have more recently dis- 

 covered it in unusually well preserved sections of Lepidoden- 

 dron selaginoides and of L. Harcottrtii. The contiguous 

 transverse bars of these tubes are connected together by 

 innumerable very delicate parallel vertical threads of great 

 tenuity.* 



My cabinet contains a very well-marked Halonial 

 branch of L. WunscJiianum, in which the tracheal strands 

 of the fructigerous tubercles are of the true Halonial type. 



Youngest Twigs. 

 Primary Xylem Strand, 



K. — p. 434, Fig. la, C.N. 428. 

 Fig. 2, C.N. 428. 



Inner Cortex. 



K. Feebly represented in Fig. 2, C.N. 428. 



Outer Cortex. 



K. Fig I. Only fragmentary traces in C.N. 428 and 430, binding the 

 leaves together. 



Large Twigs or Branches. 



Medulla Still Wanting. 

 Transver&e. 



C.N. 433- 

 Vertical. 



C.N. 433, AandB. 



* This is a valuable feature ; being present in the youngest twig (See 

 C.N. 431) on which there is no medulla, as well as in all the examples in which 

 the medulla is developed, it becomes an important link in the chain of evidence 

 demonstrating that all these differences of structure merely belong to the same 

 plant in its several stages of growth and development. In some cases this 

 feature is imperfectly preserved ; but that this is due to accident is proved by the 

 fact that we sometimes find the structure most distinct in one part of a strand, 

 whilst it has wholly disappeared from another part of the same strand. 



II 



