1902] Ammidown, — Protection against Rhus-poisoning 105 



In some cases it was possible to secure specimens that still retained 

 some of the old formerly floating leaves at the tip of the long stems, 

 yet had erect stems from the same root, bearing the hairy leaves and 

 foliaceous sheaths of P. Hartwrightii. 



In early October when the water was at its lowest point, the plants 

 farthest up the bank had lost nearly all trace of the amphibium form, 

 while lower down all stages of transformation could be seen between 

 that and the plants still floating in the water, true amphibium. 



The fact that in this case the same root that produced typical P. 

 amphibium when underwater, produced typical P. Hartwrightii when 

 left exposed for a time above water, would seem to prove that P. Hart- 

 wrightii is not a distinct species but a terrestrial form of P. amphibium. 

 It is nothing unusual that this should be the case, as many other 

 species are known to take different forms under such conditions. 

 Ranunculus multijidus and its var. tcrrcstris, and Myriophyllum am- 

 biguum and its var. limosum, are illustrations of such variations. 



From the scarcity of flowers and fruit in the terrestrial plants of 

 this Polygonum, it would be inferred that the species was in its nor- 

 mal habitat when growing in water. Although P. Hartwrightii in 

 the locality where I have observed the transitions above described, 

 is obviously only a biological state of P. amphibium, this state 

 appears to become in other places the habitual form, so that it 

 requires some taxonomic recognition. It cannot be regarded as a 

 distinct species, and it may be best to call it P. amphibium, var. 

 Hartwrightii as it appears closely analogous to the varieties of 

 Ranunculus and Myriophyllum, mentioned above. — C. H. Bissell, 

 Southington, Connecticut. 



Saleratus as a Protection against Rhus-poisoning. — In the 

 matter of Ivy-poisoning, discussed by Franz Pfaff, M. I)., in the 

 March Rhodora, I have had a little experience which may be of 

 interest to those readers who have been kept from exploring rich 

 floral fields through fear of Rhus venenata, the poison Dogwood. 

 Not far from my home, on the boundary between Southbridge and 

 Charlton, Massachusetts, there is a large sphagnous tract, known as 

 Cedar Swamp. A good-sized pond lies concealed in it, and where 

 the road crosses the swamp one can from the roadside run a pole 

 down many feet without reaching bottom ; yet the tangle of roots is 

 so thick that by exercising a little care it is possible to walk upon 



