XLVHl] PREPINUS 403 



As the choice of the name Prepinus implies, Jeffrey regards 

 the type of foliage-shoot represented by these species as the direct 

 ancestor of the leaf-spurs of recent Pines. The short shoots of 

 Prepinus are smaller than those of existing species of Pinus, but 

 in the numerous and spirally arranged leaves they resemble those 

 of Cedrus and Larix. Anatomically the fossil leaves differ widely 

 from any Abietineous types, and were it not for the occurrence of 

 true Pine needles in association with Prepinus, which to some 

 extent bridge the gap between Prepinus and Pinus, one might be 

 sceptical with regard to the close affinity of Prepinus to recent 

 Pines. Jeffrey compares the structure of the leaf of P. statensis 

 with that of some leaves of Cordaites, but the agreement is probably 

 not so close as Dr Stopes' description 1 , quoted by Jeffrey, suggests. 

 Jeffrey 2 regards the short shoots of Pinus and other Abietineae 

 as a primitive attribute of the Coniferous stock and as one of several 

 reasons for believing the Abietineae to be the oldest tribe of 

 Conifers. Prof. Thomson 3 has recently discussed the value of the 

 evidence based on the short shoots of Pinus and Prepinus and 

 comes to the conclusion that the foliage-spurs of Pinus are 

 specialised shoots and do not belong to the category of primitive 

 forms. In Cedrus, Larix, and Pseudolarix the leaves are spirally 

 disposed on the short shoots, while in Pinus they are fewer and 

 cyclic. The frequent occurrence of more than the normal number 

 of leaves on the foliage-spurs of Pinus has already been mentioned : 

 in healthy plants supernumerary foliage-leaves are not uncommon 

 and an increase in the number of needles is also induced by 

 wounding. The spirally arranged scale-leaves below the whorled 

 leaves on a short shoot of Pinus are homologous with the scale- 

 leaves on ordinary branches, and on seedling Pines they are re- 

 placed by the primordial leaves: transitional forms occur between 

 these three forms of leaf. The persistent short shoots of Cedrus, 

 rix, and Pseudolarix, as also of Ginkgo, are regarded as the more 

 primitive condition as compared with the deciduous nature of the 

 cyclic foliage-shoots of Pinus. Thomson notes that short shoots 

 of Pinus may proliferate like those of Cedrus and Larix. He 

 concludes that ancestrally 'the leaves of the Pines were spirally 

 arranged on ordinary branches and that the spur is derived from 

 1 Slopes (03). 2 Jeffrey (JO 2 ) p. 331. 3 Thomson (14). 



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