CHAPTER XV. 



STRUCTURE OF FOLIAGE AND OF FLORAL LEAVES TERMINA- 

 TIONS OF THE VASCULAR BUNDLES FALL OF THE LEAF. 



PRINCIPAL MATERIALS USED. 



Leaves of Ruta graveoleiis ; fresh ; also in alcohol. Or, of Helleborus niger, 



Syringa vulgaris, or Eucalyptus globulus. 

 Leaves of Fagus sylvatica ; fresh, or in alcohol. 

 Similar leaves, grown in shade and in bright sun, selected for comparison, 



and placed at once in alcohol. 

 Petals of Verbascum nigrum, or Papaver RJiceas, fresh ; or Siletie inflate, 



Azalea indica, Mimulus luteus ; or standard of Laburnum ; fresh, or 



in alcohol. 



Leaves of Impatiens parviflora ; in absolute alcohol. 

 Leaf-bases of JEsculus, or other plant, prior to fall ; in alcohol. 



PRINCIPAL REAGENTS USED. 



Turpentine and creosote (3 : 1), or Chloral hydrate in water (8 : 5) Acetic 

 methyl green. 



Leaf of Ruta graveolens. By the aid of a series of selected 

 examples we will now endeavour to make ourselves acquainted 

 with the structure of leaves. We will first deal with foliage 

 leaves, and especially those kinds which exhibit the most pro- 

 found differentiation in their inner structure. Our first example 

 shall be the garden Rue (Ruta graveolens), the leaves of which 

 also usually remain fresh during the winter. The leaves of this 

 plant are bipinnate, the leaflets obovate. Held towards the light, 

 these leaflets show bright spots ; these are the internal glands, 

 filled with etherial oil, which are found in the inner tissue of the 

 leaf, and to the oil contained in which the leaf owes its strong 

 smell when bruised. 1 We take in the first place surface views 



1 It is well, however, to bear in mind that such oil-glands, though present 

 in very many kinds of leaves, are not a usual constituent of structure. [Eo.] 



(189) 



