THE PRINCIPLE OF COHESION. 67 



Above the ovary-cells, at the base and thicker part of the 

 stj'le, a section (Fig. 13, d) shows five solid circular buttresses, 

 the tissue of which is continuous with the central paren- 

 chyma, in the middle of which a lacuna (f) is formed by 

 rupture. In the depression between the buttresses, a small 

 portion of the style and conducting tissue forms a bridge, 

 as in Fig. 13, d, showing a cavity below it. 



It is in this homogeneous mass of ground tissue that we 

 have a complete fusion of the hypertrophied borders of the 

 carpels which have thus entirely lost their individuality. 

 The axis proper disappeared as soon as the spiral vessels 

 became oriented, as in Fig. 13, a. 



Hence the dotted lines radiating from the centre (c) 

 mark the ideal boundary of each carpel, and the line across 

 the base of the ovary-cell is the place Avhere rupture will 

 take place when the fruit is mature. The column, or so- 

 called "carpophore," remaining is therefore entirely carpellary 

 in its origin. 



The third method by which the tracheae pass from one 

 side to the other of a cord is partly seen in the preceding ; 

 and I suspect that this is the commonest method of all ; for 

 though, when axial, the cord has its spiral vessels fixed at 

 the inner angle, as soon as a change of position occurs or 

 whenever it has to branch, the fixity of the position of the 

 trachejB becomes relaxed, and they readily become enveloped 

 in the rest of the tissue of the cord, and so pass from one 

 side to the other with perfect facility, as will be seen in the 

 case of the Ivy. 



When a syncarpous pistil has its ovary inferior — that is, 

 imbedded in the receptacular tube — the real state of cohesion 

 between the several carpels is masked in consequence of 

 their partially undifferentiated state ; the ovaries of which 

 then have the appearance of being simply isolated cavities 



