OF LOWER GREENSANJ) PLANTS. 79 



The question of date of the first appearance of the Abietinea) 

 lias aroused ranch interest and controversy. To establish his 

 view that the Pinus-tyyc is the most ancient conifer stock, Prof. 

 Jeffrey and his school have sought for confirmation among fossils, 

 and have in the past made much of the supposed existence of 

 two forms of Pityoxylon in the Palaeozoic. Various writers have 

 doubted the validity of the statements based on the two fossils in 

 question Pittjoxylon Chasense from the Permian and P. Con- 

 wentzianum from the Carboniferous (see, for example, Gothan, 

 19 10 A). The matter has been finally cleared up by Thomson 

 & Allin (1912), who demonstrate the fact that neither of these 

 specimens is what it has been supposed to be, and that there is 

 no evidence of the existence of Pltyoxyton in the Palaeozoic. 



On the other hand, though Prof. Jeffrey has claimed this 

 antiquity for Piti/oxylon, he and his pupils have been content to 

 conclude that the structures of the modern Pinus are of com- 

 paratively recent date, and they state (see Jeffrey & Chrysler, 

 1900, and others) that the ray-tracheids of the modern pines 

 evolved in the Tertiary or Upper Cretaceous (see also p. 98, etc., 

 where ray-tracheids of a much earlier date are described). 



Notwithstanding the fact that the described Palaeozoic Abic- 

 tineyc have been discredited, and no reliable records of the 

 existence of this family in the Palaeozoic have been substituted, 

 Prof. Jeffrey and his pupils do not discard their main argument, 

 which was originally based on the now-discredited records. 



At the same time, Piuus-likc forms are undoubtedly very 

 ancient, for, as Fliche and Zeiller (1905) have shown, they seem 

 to have been already differentiated in the Jurassic, where it 

 appears possible to recognise tho two main sections of the 

 modern genus Pinus, viz. Pinaster, the " hard pines," and 

 Strobus, the "soft pines." 



The difficulties in determining to which living genus the 

 forms of the various Pityoxylons may be related, are naturally 

 multiplied by the great distance in time which separates these 

 fossil forms from those now living. Woods which show many 

 features generally regarded as characteristic of Pinus may yet 

 represent the ancestors of other living tribes. For example, 

 interspersed ray-tracheids, wLich arc a fairly characteristic 

 feature of Pinus, have been detected in a wounded species of 

 Abies, and the conclusion drawn from his investigations by 



