BRIEFER ARTICLES. 
POTAMOGETON ROBBINSII. 
(WITH PLATE XV) 
THIS pondweed, first described by Oakes in 1841, is the rarest of 
the North American speciés to fruit, unless we except P. interruptus 
Kitaibel, which bears floral spikes quite freely, but is not known to 
mature fruit in this country, though it does in Europe. The principal 
mode of propagation of P. Robbinsii is by fragments of the stems, 
"hich root freely in the muddy bottoms of ponds and lakes where it 
Sows, often forming dense patches covering considerable areas. Dr. 
mas Morong writes with regard to its fruiting as follows: “Very 
‘arely, in years when the waters are low, the flowering spikes rise above 
Surface and perfect a few fruits. Dr. Robbins never saw but one 
fruit, which was collected many years ago in Oregon by Hall, and this 
oat in two, Prof. D. C. Eaton taking one half and Dr. Robbins 
me other. In the year 1880 Mr. Faxon had the good fortune to 
aa fruiting specimens in Jamaica Pond, Massachusetts. 
: is very t a T have never known another instance, although the plant 
a" _ In the localities where it occurs.’” 
ZY 00d fortune in 1880 to find it fruiting in the Chesago 
a hy — City, Minnesota, and a number of specimens were 
This was in early September. Twice before during the same 
Sago) 
* plants were collected in the latter part of July in northern 
a isan, at Republic, and in Goose lake near Negaunee. The speci- 
Men from 
Bpriority ay has « spike of fruit well formed, but immature. The 
'0 those hith ne plants from the Chesago lakes, compared 
Prepar 7% to figured, has led me to have the accompanying plate 
; Upper parts pi Se aeny represents the average of the fruiting a 
: SOO, ot bein: “ aterm, the lower very leafy portion, or that of barren 
a ‘ety pani te represented. The specimens show an inflorescence 
- The ag the fruiting portion of the stems being 10 to I ae 
tag NAidacee of North America, Mem. Torr. Bot. Club 3: 54. 1893. 
