M'Nab — Remarks on the Leaves 0/ certain Coniferce. 209 



XXXII. — Eemaeks oisr the SxinTCTrrRE of the leaves of ceetaik 

 Coi^rFEiLai:. By W. E. M'JSTae, M. D., Edinburgh, Professor of 

 Botany, Eoyal College of Science for Ireland. (Witli Plate 23.) 



[Read June 1 4, 1875.] 



Ijt a Thesis wHcIl was presented to the Pacnlty of Science, Paris, 

 and published last year. Dr. C. E. Bertrand describes the comparative 

 anatomy of the stems and leaves of the Gnetacese and Coniferee. In 

 his descriptions Bertrand gives anatomical characters^ by which sub- 

 genera may be readily separated, and also gives tables by ■which, 

 to identify the species. BeKeving that, in one or two respects, 

 Bertrand has come to erroneous conclusions, I determined to re-inves- 

 tigate certain poiats which I considered of importance. In doing so 

 I had the great advantage of having access to the collection of Coni- 

 ferse at the Eoyal Botanic Garden, Edinbui'gh, where most of the 

 rare and valuable JN'oi'th American species are carefully cultivated. 

 "We are certainly much indebted to Bertrand for pointing out that 

 valuable characters can be got by anatomical investigation of the 

 leaves of Pines. To the nurseryman who has chiefly to do with 

 small plants without cones, any good method of determining species by 

 the foliage must be welcome. While, however, I acknowledge the 

 value of such anatomical characters, I do not think we can place im- 

 plicit confidence in them alone ; but that, when taken along with 

 other characters, they are of the highest value. It is chiefly by 

 making transverse sections of the leaf that the investigation is to 

 be carried on. Yeiy thin slices are to be taken from the middle 

 of the leaf, care being taken to have the sections in the proper 

 plane. All the sections I have examined were placed at once in dilute 

 glycerine ; and, in nearly all cases, the perfectly fresh leaf was used. 

 The chief points to obsei've in the sections are: — 1st, the nature of 

 the fibro-vascular bundles or midrib ; 2nd, the sheath of the fibro- 

 vascular bundles ; 3rd, the resia canal or canals ; 4th, the thickened 

 cells or hypoderma belonging to the ground-tissue, and placed below 

 the epidermis, but not belonging to it ; 5th, the parenchyma of the 

 ground-tissue ; 6th, the epidermis, with its cuticle ; and 7th, the 

 arrangement of the stomata ; this last, however, requiring the examina- 

 tion of the upper and under surfaces of the leaf in addition. 



My attention was first directed to Bertrand' s sub-genus Tsuga, 

 which includes — Pinus Fattoniana, canadensis, Ifertensiana, Sfc. I 

 think it is best to follow Parlatore in his definition of the genus Pinus ; 

 but I would limit Parlatore' s section Tsuga, and use it in the restricted 

 sense in which Carrierc andBcrtrand employ it. In Parlatore's Couiferse 

 (De CandoUe Prod., vol. xvi., pars 2), the section VI. Tsuga Endl. 

 Pari, is used to include : — Tsuga Carr., Ketcleeria Carr., and Pseudo- 



R. I. A. PKOC, 3ER. II., VOL. II., SCIENCE. 2 F 



