PHYSIOLOGY OF TIIE LEAVES OF CERTAIN CONIFERS. 547 



Note on the Eelations between Morphology and Physiolog 



the Leaves of certain Conifers. By Maxwell T. Masters, 

 M.D., F.K.S., F.L.S. 



[Eead December 4, 1879.] 



The following remarks have reference to the form, arrangement, 

 direction, internal structure, and function of the leaves of the 

 Silver Firs (Abies of Continental, Picea of British writers) as 

 contrasted with those of the Spruce Firs (Picea of Continental, 

 Abies of British writers). 



For my present purpose it will not be necessary to enter at 

 full length into details, which can be obtained from easily acces- 

 sible works. 



The outward characteristics are given in all descriptive works 

 treating of Conifers; the physiology of the leaf in general is 

 sketched more or less fully in the text-books. Two special 

 memoirs, however, demand more direct notice at my hands 

 that of M. C. E. Bertrand, "Anatomie comparee des tiges et des 

 feuilles chez les Gnetacees et les Coniferes,"* and that of Prof. 

 M'JNab, entitled "A Eevision of the Species of Abies "t. 



The Pulvini. — In the Spruces the surface of the shoots is 

 marked with very prominent pulvini, which have been taken as 

 points of discrimination between species by Zuccarini and others. 

 On a superficial examination, it would seem as if these pulvini 

 were the " decurrent " bases of the leaves — that the sheathing 

 portion of the leaf, in other words, was adherent to or inseparate, 

 for a short distance above its point of origin, from the axis. A 

 closer examination, however, will show that the central fibro- 

 vascular bundle of the leaf passes direct from the axis into the 

 leaf. In a transverse section of a young shoot of Picea ajanensis 

 a zone of wood may be seen surrounding the central pith. 

 Around the wood is a thick layer of meristem-cells filled with 

 chlorophyll. Traversing this zone are a number of resin-canals 

 disposed in a ring. The outer portion of this layer of cells deve- 

 lops into a phellogen layer, outside which is a thick corky invest- 

 ment consisting of loose parenchyma w r hose cells are destitute of 

 chlorophyll, and which forms the mass of the pulvini. Outside 

 this is a layer of hypoderm-cells stained yellow by the addition of 

 potash, and consisting of a single series, except in the recesses 



* Annales des Sciences Naturelles, 5th ser. torn. xx. (1874). 



t Proceedings of the Eoyal Irish Academy, 2nd ser. vol. ii. p. 073 (187G). 



