148 Professor Alexander Dickson on the 



EXPLANATIOX OF PLATES. 



Plate IX. (figs. 1, 2, and 3). 



Fig. 1. Photo-lithograpli * of small plant (from rhizome-division) of 

 Ruscus androgynus ; showing "radical" Foliage-leaves (fl.), and weak 

 aerial stem (as) bearing Cladodes (cl). 



Fig. 2. Outline figure of a similar plant. From a photograph. 



Fig. 3. Outline figure of transverse section from about the middle of the 

 petiole of the Foliage-leaf, showing arrangement of the vascular 

 bundles, and disposition of the fibro-vascular elements. In each 

 bundle are to be noted : (1) the Phloem (jjh), indicated by dotted shad- 

 ing, and (2) the Xylem (x) ; the whole being surrounded by a Bundle- 

 slieath of indurated prosenchyma (bs). m= Ground tissue, or Matrix, 

 ep = Epidermis. The mesial bundle at the lower part of the figure is 

 continued up into the lamina as the midrib ; while the others spread 

 themselves out and subdiWde, to run in the lateral halves of the 

 lamina, where they so adjust themselves to its surfaces as to have 

 their Xylem directed upwards. At each of the upper comers of the 

 section, is a rudimentary bundle, wholly fibrous. 



Plate X. 



Fig. 1. Section of Cladode of Ruscus androgyny^, at right angles to the 

 surface, and across one of the stronger longitudinal veins. 



se = Moi'phologically-upper epidermis, in which two stomata are 



to be noted. 

 sp = ^lorphologically-upper chlorophyll-parenchyma. 

 mp — MidtUe layer of colourless parenchyma. 

 if = Morphologically-lower chlorophyll-parenchyma. 

 ie = Morphologically-lower epidermis, destitute of stomata. 

 bs = Bundle-sheath of indurated prosenchyma. 

 2yh = Phloem (here consisting of soft-bast), directed towards the 

 morphologically-itpper surface of the Cladode. 

 X = Xylem, directed towards the morphologically-Zower surface of 

 the Cladode. 

 Fig. 2. Portion of epidermis from morphologically-upper surfe,ce of 



Cladode, showing numerous stomata. 

 Fig. 3. Portion of epidermis from morphologically-lower surface of 

 Cladode, destitute of stomata. In tliis and in the last figure, the direc- 

 tion of the long axis of the Cladode is across the plate. 



* I may here draw attention to the methods of production of the figures in 

 these plates. 



In Plate IX., fig. 1 is not a drawing, but is a photo-lithograph from the 

 plant direct. The "grain" in the lithograph is obtained by interposition 

 of a "stippled" transparent film between the photographic "negative" and 

 the " transfer." 



In Plate IX. , fig. 2 is a photo-lithograph from an outline-drawing obtained 

 from a photograph, by a process which I have elsewhere described, but which 

 it may be useful for me again to refer to. A paper-print is taken from the 

 "negative ; " the outlines on this print are carefully gone over with a fine pen 

 and Indian ink or other black paint ; the photograph is then obliterated by 

 washing with cyanide of potassium solution, lea\'ing the black outline on the 

 now white paper ; and from this outline-figure, after any necessary "touching- 

 up," a photo-lithograph is made to the desired scale. 



In Plate IX., fig. 3, and in Plates X. and XI. all the figures, are photo-Iitho- 

 gi-aphic reductions from pen and ink drawings made with help of camera lu^ida. 



