MIDDLESEX FLOKA. 87 



P. Hydropiper, L. SMARTWEED. WATER-PEPPER. 

 Common. July-Sept. 



P. acre, HBK. WATER SMARTWEED. 



Medford (G-. E. Davenport) ; Weston (F. S. Collins) ; Framingham 

 (Rev. J. H. Temple) ; Concord (Minot Pratt) ; Dunstable (Dr. C. 

 W. Swan). Not very common. July-Sept. 



P. hydropiperoides, Michx. MILD WATER-PEPPER. 

 Rather common. July-Sept. 



P. Mulhenbergii, Wats. (P. amphibium, L., var. terrestre, 

 Willd., Man.) 

 Rather common. Aug.-Sept. 



P. Hartwrightii, Gray. 



Chelmsford (Dr. C. W. Swan) ; Fresh Pond, Cambridge (Dr. W. G-. 

 Farlow). Not common. Aug-Sept. 



" Perennial, closely allied to the two preceding species, (P. am- 

 phibium and P. Muhlenbergii) growing usually in mud, the as- 

 cending stems rooting at base and very leafy ; differing from the 

 form of P. (amphibium?) growing in like localities, by being more 

 or less rough-hairy, at least on the sheaths and bracts, the former 

 ciliate and often with abruptly spreading foliaceous borders; 

 leaves rather narrow, 2 to 7 inches long, on very short petioles, 

 adnate to the middle of the sheath." Bot. Cal. 



P. articulatum, L. JOINTWEED. 

 Common. Aug.-Sept. 



P. aviculare, L. KNOTGRASS. 

 Very common. July-Sept. 



P. erectum, L. (P. aviculare, L., var. erectum, Roth, Man.) 

 Not uncommon. July-Sept. 



P. ramosissimum, Michx. 



Watertown (C. E. Perkins) ; Medford (C. E. Faxon) ; So. Natick 

 (F. S. Collins). Scarce, except along salt marshes. July-Sept. 



P, tenue, Michx. 

 Frequent. Aug.-Sept. 



P. arifolium, L. HALBERD-LEAVED TEAR- THUMB. 

 Not reported from the northern and northwestern towns, but rather 

 common elsewhere in the county. Aug.-Sept. 



P. sagittatum, L. ARROW-LEAVED TEAR-THUMB. 

 Common. Aug.-Sept. 



P. CONVOLVULUS, L. BLACK BINDWEED. 

 Common. Aug.-Sept. Nat. from Eu. 



P. cilinode, Michx. 



Ashby (Dr. C. W. Swan) ; Waltham List; Newton (C. J. Sprague). 

 Scarce. 



