22 STRONG DRINK AND TOBACCO SMOKE. 



a new leaf, was produced, a solid plate of tissue (dia- 

 phragm) remains for a time ; Lut as the diameter of each 

 node of the stem increases, the central portion not being 

 renewed, the stem in time becomes hollow. 



In the centre of the lobed inflorescence (fig. 19, a) 

 may be clearly distinguished, even at this early stage of 

 its development, the flower and fruit-bearing stalk ; at the 

 base of this again is the last undeveloped joint of the 

 stem, and beneath this the solid mass from which other 

 leaves and internodes of the stem will be formed. 



Plate 2, figs. 14 and 15, represent a horizontal and 

 a vertical section of the mature green stem of bar- 

 lev. The sections are not cut across or thi'oucrh the 

 middle of the last formed diaphragm, for then we 

 should have a solid mass without the intervening 

 space represented by the white ring which here sepa- 

 rates the outer developing stem from the inner more 

 immature portion, but at a point just above d (Plate 3, 

 fig. 19). 



The structure of the stem is well seen in the vertical 

 section at Plate 4, fig. 25, where the spiral vessels are seen 

 lying amongst the woody and dotted fibres, whilst the 

 inner circular cells of the pith are gradually being torn 

 asunder by the horizontal expansion of the stem at the 

 internode above. The development of hairs on the outer 

 skin may be easily traced on the young green stem. Jn 

 early growth they have the appearance of minute knobs 

 (Plate 2, fig. 16). AVhen they are mature, and have 

 become silicated on their outer surfaces, they have a more 



