4 Weiss, The Parichnos in the Lepidodendracece. 



T. G. Hill (:o6) of the occurrence of similar structures in 

 the leaves of recent Lycopodiales, more especially in the 

 sporophylls, and these structures he considers to be 

 phylogenetically identical with the parichnos of the 

 Lepidodendracese. Potonie ('99) had already drawn 

 attention to the resemblance between the mucilage 

 passages of Lycopodium and the parichnos of Lepido- 

 dendron* though he considered the function of the two 

 sets of organs to be different. 



Hill has extended the comparison to Lsoetes hystrix 

 where a double strand of tissue comparable with the 

 parichnos exists. In Lycopodimn the mucilage duct is 

 single. This does not however lessen the possibility 

 of their being homologous structures, as Maslen ('99) 

 has found Lepidostrobus, the cone of Lepidodendron, to 

 have an unbranched parichnos strand. 



As Hill mentions, the state of preservation of the 

 parichnos strand varies considerably. In some cases we 

 have very well preserved parenchymatous cells as seen in 

 the figures of Lepidodendron selaginoides in M. Hovelacque's 

 Memoir, and still more so in the longitudinal section 

 mentioned above, and figured in the Trans, of the Linnean 

 Society (Weiss, :03). In other cases, such as those figured 

 by Mr. Maslen, the parichnos strand is represented by 

 empty canals showing no cellular tissue at all. 



As this latter is also the condition in the mature 

 tissues of those living Lycopodiacese in which secretory 

 strands have been observed, while the young organs have 

 a very definite tissue in this position, Mr. Hill concludes 

 that in fossil forms, too, the empty canal is the mature 

 structure, while the well preserved condition represents 

 the immature stage. This might possibly apply to the 

 parichnos strands occurring in the sporophylls, but as 

 * Potonie ('99), p. 239. 



