243 



different are they in general appearance. Each of them has re- 

 ceived a varietal name, but they can hardly be considered as any- 

 thing more than forms or states, as they readily run into each 

 other when the conditions change. 



The type of Rafinesque, commonly called by late authors var. 

 liinosiim, is entirely terrestrial, rooting in the mud upon the 

 shore, 2 to 4 cm. high, leaves much longer than the fruit, alter- 

 nate, linear, and entire or more commonly pectinate, sometimes 

 pinnatifid. Fruit minute, slightly more than i mm. long and i 

 mm. or less in breadth. Carpels usually smooth, sometimes a 

 little rough, the groove small. Petals four, purplish. Stamens 

 four. This form appears to be the offspring of the floating plant 

 which often roots in the mud where it is cast ashore, and sends 

 up an erect flowering stem, frequently leaving traces of the old 

 submerged leaves below the rooting node. 



The form called M. ainbignum var. natans by Dr. Gray (Man. 

 Ed. I, p. 140) and which he seems to have considered the type, is 

 intermediate between the type and the so-called var. capillaceiim. 

 It usually occurs in still, shallow water, with a spike of flowers 

 and the typical floral leaves above the surface, and subverticillate 

 or, more commonly, scattered pinnatifid leaves beneath ; the divi- 

 sions are few. On specimens of this from the herbarium of Mr. 

 Oakes, marked by him M. capillaceum, Nutt., I find spikes nearly 

 30 cm. long. When botanizing on Nantucket in the summer of 

 1887, I found these aquatic forms together in some of the small 

 ponds, growing in such profusion that they were literally in heaps. 

 A note sent to Mrs. Owen, and published on page 26 of her in- 

 teresting catalogue of the plants of the island, will show how inti- 

 mately associated they are. 



" In both these ponds the plant is at first var. capillacetim 

 while immersed, but very soon it gets its head above water and 

 immediately forms pectinate leaves — that is becomes the type as 

 described in Gray's Manual. I have plenty of specimens in both 

 conditions Avhich grew together." 



The form called M. ambigiaimhy Nutt. (Gen. 2, 213) and M. 

 ambigjimn, var. capillaceum by Torr. & Gray (Fl. N. A. i, 543) and 

 other authors, is commonly a deep water plant, entirely submerged. 

 Stems long, widely branching, very plumose when growing, leaves 



