XLIIl] ABIETINBAB 155 



bears 2 needles plano-convex in section. In P. monophylla (fig. 694, D) each 

 shoot has usually a single sharp-pomted cylindrical leaf 4 cm. long. Three- 

 needled Pines occur in N. America and the Himalayas but not in Europe. 

 In P. Cemhra, P. pence (the only European examples), P. Strobus, P. excelsa 

 (fig. 704), P. koraiensis, etc., the short shoots bear 5 needles and each is trian- 

 gular. Thomson' regards the dwarf -shoot of Pinus as a derivative of a longer 

 shoot with spirally disposed needles : he has recently described examples of 

 dwarf-shoots in recent Pines bearing an abnormally large number of leaves. 

 In P. silvestris shoots with 3 leaves are not uncommon : in P. excelsa wounding 

 caused the development of as many as 15 needles on a single dwarf-shoot. 

 Jeffrey, on the other hand, regards the spur-shoot as a primitive attribute of 

 the coniferous stock. The length of the leaf varies considerably and may 

 reach 30 cm. ; the margin is generally entire, but in P. Cembra the apical 

 portion is finely serrate. The structure of Pine leaves^ is well known, but 

 reference may be made to the twin bundles in hard Pines, a distinction from the 

 single strand in the soft Pines', the presence of a weU-defined endodermis (fig. 694, 

 D, e) and the infoldings of the chlorenchyma*. There are two types of cone, 

 that of the Pinaster group in which the distal end of the woody seminiferous 

 scale is more or less pyramidal and has a central umbo (of. fig. 785), prolonged 

 in some species, P. ponderosa^, P. Jeffreyi^, etc., into a short recurved spine 

 or, in P. Coulieri, into a large curved spinous process. Another type, illus- 

 trated by the Strobus group, is distinguished by the flatter imbricate scales 

 with the umbo at the tip of the free rounded margin (fig. 704). The cones of 

 the latter type resemble those of Picea. The variation in the size and form of 

 cones from the same tree in Pinus excelsa is worthy of notice from a palaeo- 

 botanical standpoint'. 



Cedrus. The more slender needles of Cedrus, most of which occur in 

 clusters on short shoots, are approximately triangular in section (fig. 694, E) 

 and have a single bundle and two canals next the lower epidermis. The 

 persistent leaf- bases resemble those of Tsuga and Picea (fig. 706, B, D). Canals, 

 though not normally present in the wood, are induced by wounding ; xylem- 

 parenchyma may occur in the late summer-wood and ray-tracheids are present, 

 but less prominent than in Pines and some other genera. The deciduous 

 nature of the mature cone-scales would lead one to expect their preservation 

 as fossils. A characteristic feature of the cones is the presence of radially 

 disposed lines normal to the edge of the sporophyUs^. Larix. The narrow 

 linear decurrent leaves, keeled on the lower surface, have a resin- canal close 



1 Thomson (14). 



' Zang (04) attempts to classify Pine leaves on the basis of anatomy. 

 ^ For anatomical features of hard and soft Pines, see Holden, R. (13'); Jeffrey 

 and Chrysler (06). 



* Kirchner, Loew, and Schroter (06) figs. 188, 222, etc. 



5 Gard. Chron. Nov. 15, 1890, pp. 561, 569. 



' Ibid. March 23, 1889. ' Bommer (03) B. Pis. ii., iv. 



8 Fliche (96) p. 86. 



