Il8 DR. J. W. HESLOP HARRISON ON 



acting as an outlet for the Fleets, it loses its stagnant 

 character to a great extent although it never manifests any 

 definite current unless the locks are open — an event of little 

 frequency. By virtue of a slight tidal backwash on such 

 occasions, it becomes somewhat brackish near its exit ; this 

 quality it loses by degrees as we proceed from the locks 

 toward Holme Fleet. 



Its Flora, whilst lacking in wealth of species, amply makes 

 up for the deficiency by the rapidity with which it responds 

 to the changing conditions ; it thus deserves our closest 

 attention. 



Westward, of the plants of taller growth, Glycerin aquatica 

 assumes domi nancy, quickly to be replaced by Scirpus 

 marititinis as we advance towards the Fleets ; this position 

 the latter plant maintains for great distances only yielding, 

 and that seldom, to Ca7-ex vulpiua. Whether Glycerin or 

 Scirpus is paramount they are alike enveloped in summer by 

 a green mantle oi Lemna minor, locally displaced by Callitriche. 

 .The other associated plants are few ; Alisvia plantago- 

 aqjtatica, Ramincubts sceleratus and Carex vulpiua alone being 

 powerful enough to penetrate through and withstand the 

 smothering carpet of Lemna — 2. layer effectually repressing 

 the growth of any form oi Ranunculus aquaiilis (agg.). That 

 R. sceleratus should succeed where its congeners fail is 

 attributable directly to its biennial* character, all its vegeta- 

 tive activities taking place when Lemna is more or less 

 dormant. When Lemna carpets the lode, the flowering 

 shoots of R. sceleratus are far beyond its stifling action. 

 That Lemna is solely responsible for the inhibition of 

 Ranunculus hetcrophyllus can be demonstrated easily by its 

 ready appearance and instant success wherever cattle, in mak- 

 ing watering places, hurl aside the Duckweed. To the same 

 failure of Lemna, owing to its overshadowing by Carex 

 vulpiua, we have to assign the luxuriance of Alisma when that 

 latter plant prevails. 



* Despite the statements of Bentham and other authors as to the annual 

 character of this plant it is always a biennial with us, nu mailer what 

 occurs elsewhere. 



