54 THE STRUCTURE OF FLOWERS. 



CHAPTER YI. 



THE PRINCIPLE OF COHESION — Continued. 



Cohesion op the Sepals, or Gamosepalous Calyx. — This is 

 congenital, and may be free, as in the Carnation and Primrose, 

 or associated with a " receptacular tube," as in Leguminosoi 

 and Rosacece. 



As sepals mostly I'epresent the petioles of leaves, the 

 tubular part of a gamosepalous calyx consists really of the 

 fusion of the expanded petioles, the teeth of the limb being 

 all that remains to represent the blades which are usually 

 suppressed. The main fibro-vascular cords correspond to 

 the mid-ribs, while the interspaces are either without additional 

 " marginal " cords, as in the Primrose, or with single or double 

 cords in the line of junction, as in the Labiatce ; or they may 

 be covered with anastoraozing reticulations without any linear 

 cord at all, as in Mimulus. 



With regard to the presence of linear cords in the line of 

 suture, if there be five sepals, there will be at least ten ribs 

 to the calyx ; i.e., if there be only one marginal cord ; but 

 as there are two margins which cohere, they may have a 

 separate cord apiece ; and then there may result fifteen cords 

 in all. Thus Stacliys has five dorsal cords with barely traces 

 of five marginal ones ; Ballota has ten, and Nepeta fifteen. 



The above arrangements may be modified by the separa- 

 tion of the two marginal cords in certain places but not in 



