88 ROYAL SOCIETY OF CANADA 



end and bordered pits at the other.^ More reeently Williamsou has 

 sliown that a re<,nUar transition from one to the otiier form, occurs in 

 the wood of Dadoxyk)n and DietyoxyUm, and lie riglitly attaches im- 

 portance to tiiese facts as showing the derivation of pitted structure 

 from scalariforni.- At the same time, however, he falls into the error 

 of misinterpreting certain stnictural features, and is thus led to wrong 

 conclusions upon which he erects a new genus distinguished from 

 Dadoxylon l>y details of structure in the bordered pit. It is not my 

 j)urpose to discuss this aspect of the question at length on the present 

 occasion, but it must be pointed out tliat the simple pits "without a 

 central jiore," which he regards las the essential characteristic ol" 

 Dadoxylon, have without much doubt originated either in conditions of 

 extreme decny, or in mechanical treatment incident to preparation of 

 t;iie sections, one or both. My own studies have shown several instances 

 where a similar interpretation of appearance could be made, but in every 

 case a more searching examination lia.s always disclosed the true nature 

 of the appearance thus ])resented. Such structural transitions as have 

 ju6t been shown to occur, are of the greatest interest and importance 

 from a phylogenetic ]xiint of view. They are what one might reasonably 

 look for upon the hypothesis that these woods are the most primitive 

 Gymnospenns, and they sene to throw much light upon the origin and 

 relationships of the various vascular elements in the higher plants, both 

 Angiosperms and Gymnospenns. 



The typical structure of the bordered pit Ln these plants is too well 

 known to require explanation or amplification lat this time, since it is 

 correctly given in all the diagnoses by leading authorities, but by way 

 of rc<?apitulation, it may be well to state that the pits are generally 

 hexagonal and ])rovided with an oblong or narrowly lenticular, diagonal 

 pore which is three-fourths the diameter of the pit, or more (tig. 11 and 

 18). When the number of rows diminishes to one, the pits commonly 

 assume a more oval form but remain more or less compressed ; and a 

 still further modification appears in the separation of the pits to such 

 an extent that tliey become round, as may be seen in ArUucaria where 

 such transitional forms occur. Kraus has employed these facts as the 

 l)asis of classification.'' distinguishing l)etween certain genera which 

 show on the one liand " Fori rotundi. vel contiguitate polygoni," and 

 on the other hand " Fori runipressi, nhlongi." 



' Jn'l Lin. See, 1840. 



• M. Mlc. Jn'l, 1869, 67-70. 



' Schimper, Pal. Veg., 370. 



