DESCRIPTIYE CATALOGUE 



however, as they do not appear to have the rays well enough 

 preserved for adequate illustration or description. Regarding 

 the best of them, P. infracretaceum, Fliche says : " Ces rayons 

 sont formes de cellules rectangulaires, pre^entant souvent d'une 

 facon tres nette Ic gros pore unique caracteristique, chez les pins 

 actuels, de la section des Pinaster, mais on ne voit point les 

 tracheides a parois en zigzag, qui dans le genre actuel les accom- 

 pagnent constamment." P. Argotinense has also uniform rays, 

 without ray-tracheids ; while P. Thomasi is too poorly preserved 

 to make it possible to determine whether or not ray-tracheids 

 were present, the supposition being that they were not. 



Pityoxylon Holiicki, Knowlton (Rollick, 1898 D, p. 134), is 

 described very incompletely, for, as the author says, "the material 

 is too obscure to permit either accurate description or satisfac- 

 tory measurement." As the distinguishing characters are neither 

 figured nor described, it cannot be compared with the new 

 British species. 



With the minutely-described Pityoxylon (Pinus of Conwentz) 

 Natlwrsti (Conwentz, 1892) satisfactory comparison of any of 

 our species unfortunately cannot be made, for in Coruventz's 

 specimen the medullary rays are so poorly preserved that it is 

 not possible to be sure even whether or not ray-tracheids were 

 specialised, while in the new English specimens the structure of 

 the rays is well petrified. 



In Pityoxylon pinastroiJes (Kraus, 1883), on the other hand, 

 we have a specimen well enough preserved for comparison with 

 our fossils, but it is of much more recent type, and has the 

 toothed thickenings of the medullary rays characteristic of 

 the so-called " Hard Pines" that are not represented in the 

 Lower Greensand forms. 



Bailey (1911) describes an Upper Cretaceous Pityoxylon in 

 which ray-tracheids are developed. Therefrom he concludes 

 that " the distribution of ray-tracheids in our lignite confirms 

 these writers [Jeffrey & Chrysler] in their conclusion that the 

 absence of ray-tracheids is a primitive condition, but shows that 

 these structures were evolved during the latter part of the Cre- 

 taceous rather than in the beginning of the Tertiar} T . This is 

 shown by the fact that the ray-tracheids are feebly developed 

 even in the older wood of the stem, and do not occur during the 

 first ten to fifteen annual rings." Bailey assumes that his sped- 



