52 



MORPHOLOGY, OR COMPARATIVE ANATOMY. 



stem ; in some cases pliyllodes exist without true laminae (fig. 57), in 

 others the laminae are more or less developed at the summit (fig. 58). 



Striking examples of phyllodia with or without laminae are furnished 

 by various species of Acacia (figs. 57 & 101), in many of which the blade 

 is present, compound and bipinnate. 



Vagina. The sheathing portion or vagina is the only portion o 

 the petiole which is developed in certain plants, as in the Grasses 

 and Sedges (figs. 59-61), in which it forms a complete sheath to 

 the stem, and passes at once into the blade at the top : this sheath 

 is merely rolled round the stem in the Grasses ; but its margins 

 are not disunited, but form a tube, in the Sedges. The vaginal 

 petiolar region is more or less distinctly evident in many Mono- 

 cotyledonous leaves which at first sight appear to be sessile, as in 

 the Tulip, Hyacinth, &c. ; and it is generally more or less developed 

 at the base where a distinct leaf-stalk exists in this class, as in the 

 Palms and, above all, in the Musaceae. In many Dicotyledons also 

 the base of the petiole is enlarged into a sheath, as in Umbellifers 

 (fig. 62). 



Fig. 61. Fig. 62. 



Fig. 59. Fig. 60. 



Fig. 59. Leaf-sheath of a Grass, with an entire liqula, *. 

 Fig. 60. Leaf-sheath of a Grass, with a bifid ligula, *. 

 Fig. 61. Leaf- sheath of Eriophorum. 

 Fig. 62. Sheathing base of the petiole of A ngelica. 



Sometimes the petiole is winged (alate), as when a narrow 

 plate of the blade structure springs from its margins ; in certain 

 cases these wings are decurrent down (or, rather, are continuous 

 with the sides of) the stem from which the leaf arises, as in many 

 Thistles, Verbascum, &c., producing a winged or alate stem. 



Cicatrix. The petiole is ordinarily more or less distinctly jointed 

 to the stem ; and when the leaf falls, it leaves a more or less ex- 

 tensive well-defined scar upon the stem, called the cicatrice-, in 



