1883.] development of the Leaves of Pinus Silvestris L. 345 



illustrative plates, and as I am aware that this subject is even now 

 engaging the attention of others, it has seemed to me advisable to 

 publish the following preliminary account of my investigations on 

 the foliage leaves of the Scotch fir, Pinus silvestris, L. Before 

 entering upon the points of interest in their development, a few 

 remarks by way of prelude upon their position, shape, and external 

 appearance will not be out of place. The leaves of this species are 

 dimorphic; in other words the permanent elongated woody branches 

 or terminal shoots of the year produce no foliage leaves, but each of 

 them produces only a single deciduous chaffy and membranous 

 scale, i.e. cataphyllary leaf. These scales consist only of leaf- 

 sheaths without laminae, and in the axil of each a special abortive 

 and dwarf branch or shoot arises which always remains very short, 

 and this latter bears first a solitary hyaline scarious scaly leaf form- 

 ing a membranous sheath for the inferior part of the branch, and 

 then at the apex the foliage-leaves. Since the species I have 

 worked with belongs to the sub-genus Pinaster only two green 

 leaves are borne in a fascicle on each shoot ; they are destitute of 

 sheaths or stipules, they are sessile and their upper surfaces face each 

 other. They are rather long (1 — 3 inches), narrow, rigid, and 

 linear in shape and are best described as acerose, their point being 

 acute. In transverse section they are nearly semicircular, i.e. con- 

 vex beneath, and flat or very slightly channelled above. They are 

 very persistent remaining on till the third year when they fall. 

 The foliage leaves are girt at their bases by the scarious scales 

 before mentioned. I now pass to the chief features in their de- 

 velopment. 



I. Dermatogen. 



Development of the Stomata. The dermatogen cells form a 

 single layer, in outline they are polyhedral and somewhat elon- 

 gated, their long axes corresponding with that of the leaf; 

 they are rather deeper than broad and their inner faces are 

 slightly angular. They are bounded by perfectly flat walls. At 

 numerous intervals on both surfaces of the leaf, but especially 

 on the convex lower surface, a nearly cubical piece becomes 

 separated and cut off at one end of an epidermal cell by a radial 

 septum which runs in a plane transverse to the length of the 

 leaf. This segment speedily grows in extent, and becomes large 

 and conspicuous though it still retains its quadrangular form. Its 

 protoplasmic contents stain very deeply and it possesses a large 

 oval nucleus. Each of these cells constitutes the mother-cell of a 

 stoma. So far the mode of development and preparatory division 

 resembles very much that characteristic of Hyacinthus and Iris 1 . 



] Strasburgor, Inc. cit. pp. 300—304, PI. xxxv. figs. 1—14. 



