24 



FOLIATION. 



even in species included in the same genus. Some of the more easily 

 observed forms may be here mentioned as they afford in many 

 cases a simple mark for distinguishing the genera. 



In Finns the leaves are linear or filiform (thread-like); in some species 

 of remarkable tenuity and exceeding a foot in length (P. longifoUa, 

 P. pafu/a, P. Sabiniana) ; in others they scarcely exceed an inch in 



length (P. Parry ana, P. mono- 

 plujlla, P. Bcdfouriana). Their 

 form is modified according as 

 they are in fascicles of two 

 (geminate), three (termite), or five 

 (quinate) ; in the first named 

 they are semi-circular in section, 

 that is, they have one convex 

 and one plane side ; in the 

 other two they are triquetrul 

 (three-angled) with one convex 

 and two plane sides. Much 

 discussion has arisen respecting 

 the true nature of the "needles" 

 or adult (secondary) leaves of 

 Pines which need not be intro- 

 duced here. " The evidence 

 derived from comparative mor- 

 phology including teratology, 

 development and minute anatomy 

 is entirely in favour of the 

 view that the ' needles ' are 

 true leaves borne upon a shoot 

 whose apical development is 

 usually arrested after the forma- 

 tion of the verticil of leaves, 

 two, three or five, as the case 

 may be."* 



In the group of genera known 

 under the common name of 

 Firs (Abies, Picea, Tsuga, etc.) 

 the leaves are linear or acicular 

 (needle-shaped), flattened or 

 tetragonal (four-angled) with 

 their apex spine-tipped, acute, 

 blunt or emarginate. In some 

 species of Abies the leaves on 

 the fertile branches are different 

 in form, size and direction from 



those on the sterile (usually lowermost) branches ; this difference is notice- 

 able in A, re-phalonica in which the leaves on the cone-bearing branches 

 are acicular and spread equally on all sides, whilst those on the barren 

 branches are longer, flattened, spine-tipped and pseudo-distichous. In A. 

 Jirma the leaves on the barren branches are longer and narrower than those 

 on the fertile ones, and they are also deeply notched. In A. roncolor 



* Masters in Journ. Linn. Soc. XXA T II. 267. 



Fig. 0. Ternate leaves of Pin us radiata. 



