LECT. VIII.] STRUCTURE OF HERBACEOUS STEMS. 415 



pale green opaque bark, enclosing a transparent 

 parenchyma studded with fourteen opaque ovate 

 spots of the same colour as the bark, and having 

 a white dot in the centre of each spot (see Plate 

 8, fig. 2, A) . Placing the same slice under a mi- 

 croscope of a moderate power, we find that the 

 transparent portion is formed of hexagonal cells of 

 different sizes; and each spot consists of the divided 

 orifices of two clusters of oblong cells and entire 

 vessels, surrounding one large and several small 

 sap vessels. The bark appears to consist of a 

 cuticle and three distinct cellular bands, the cen- 

 tral one of which is filled with a green fluid, and 

 may be regarded as equivalent to the green cel- 

 lular integument in ligneous dicotyledons ; except 

 that it penetrates the outer band to the cuticle at 

 nearly equal distances (Plate 8, fig. 2, B). If we 

 take a small portion of this section, and also of 

 a longitudinal slice of the stem, and examine 

 them under the highest power of the microscope, 

 we shall find the real structure of this kind of stem 

 to be as follows. The cuticle is irregularly reti- 

 culate and streaked with green cellular lozenge- 

 shaped spots (Plate 8, fig. 3, a. a.) 9 which are the 

 processes of the middle band of the bark ; the 

 outer cortical band, or that immediately within 

 the cuticle, consists of narrow tubular cells (see 

 a. a. fig. 4, A and B. Plate 8); the second of 

 shorter and wider cells (b. b.) y filled with the green 

 secretion already noticed, and penetrating to the 



