298 



NOTES ON PONDWEEDS. 



keel. Whole plant dull olive-green, drying darker, of very vigorous 

 growth, 3-10 ft. long. 



The broad, lower leaves are submerged on the fruiting stems, 

 and on these are usually (or always?) much decayed by the time of 

 flowering. They are occasionally produced late in the summer on 

 barren shoots, and are then to be found on the same rootstock as 

 the fruit-bearing stems. Sometimes in rapid streams, which are 

 too swift to allow the flower-spikes to emerge and become fertilized, 

 they are persistent, and sometimes they are quite absent for one or 

 more seasons. These broad, 3-5-ribbed leaves are usually stem- 

 leaves, but in barren states of the plant they occur on the upper 

 branches, and then form the outer or sheatldwj leaf of each branchlet, 

 the whole of the leaves of which in such cases are often of a some- 

 what thickened, stouter growth ; rarely this state of the plant 



•produces flower-spikes, when it is, I believe, the P. Vaillandi of 

 some authors. 



In stagnant water all the branches ascend to the surface, and 

 spread out like a fan ; but in tidal rivers or running streams the 

 branchlets have a more elongate, parallel growth, and the tips of 

 the leaves rise slightly above the surface of the water, looking like 

 short blades of grass. Like all other Potamogetons, this speoies 

 bears the flower-spikes above water until fertilization has taken 

 place, when the peduncle sinks back, and the spike remains barely 

 submerged on the surface of the foliage until the fruit is full-grown ; 

 but I believe the final ripening of the fruit takes place at the bottom 

 of the water after the fruiting branchlets have rotted off. As far as 

 I have been able to observe, pondweeds vary considerably in the 

 depth at which they mature their seeds. P. natetnt sometimes 

 ripens its fruit fully exposed to the air ; P. heterophylhis bends back 

 its spikes, and the seeds are matured at the depth of two or three 

 inches; and P.praltmgm sinks to the bottom even before the fruits 

 are full-grown. I wish to call the attention of students to these 

 variations of habit, as they may possibly afford valuable diagnostic 

 characters when properly worked out. 



borne confusion has arisen in the minds of botanists through a 

 state of P. fiabellatm, named P. scopanus, having been wrongly 

 placed under P. peetinatiu as a variety of that species ; this form 

 certainly has a superficial resemblance to the latter plant in its 

 slender growth, and finely setaceous leaves ; but these leaves have 

 the structure of those of P. ji«hell„tm, and the fruit is absolutely 

 identical m character with that of the latter species. " P. scopanus " 

 is a iorm that inhabits brackish and stagnant waters : through the 

 Kindness of Mr. J. Owles, of Great Yarmouth, I have been able to 

 cultivate a salt-water form of this variety, which has very fine 

 bristle-like leaves, the internodes between which are so shortened 

 as to give the branchlets a fasciculated appearance. To this form 

 I believe the varietal name of pseiuh-marinus has been given. 

 Under cultivation in a stagnant pond I find these several forms of 

 i . jlabeUatus, while retaining their individual characteristics to 

 some extent, do certainly approximate to the fine-leaved form 

 named "icopariui," and that they do not at all approach P. 



