Observations on Gas Movement in the Rhizome ofMenyanthes trifoliataL., with Comments on the Role of the Endodermis

Abstract

SUMMARY Patterns of diffusion of oxygen in the rhizome of the aquatic Menyanthes have been investigated after the interruption of either stelar or cortical diffusion path ways. Forty-eight hours after ringing, oxygen levels in cortex, stele, and root were significantly depressed, although never to danger point. Interruption of the stele, involving also partial interruption of the cortex, was only significantly effec tive when made just above the sampling zone. The addition of M/iooo KCN to depress the metabolic uptake of oxygen, resulted as expected in higher equili brium levels of oxygen in all zones. It was shown (a) that the velocity of diffusion of oxygen across the endodermis essentially conformed to that of a process of aqueous diffusion and (b) that oxygen diffused through the cortical air-space system at about gg of its diffusion velocity in air. The diminished diffusion rate in the cortex is doubtless due to the frictional resistance imposed by the small pores which connect adjacent air cavities. An analysis has been made of the pertinent anatomical features of this rhizome, and the findings as a whole are discussed in relation to their functional and eco logical significance.