POTAMOGETONS IN RELATION TO POND CULTURE. 263 



During the season of 1913 the plants which flourished in a submerged condition 

 during the month of May gradually changed their habitat upon the withdrawal of the 

 water during June and became land forms by the first of July. At this time the tuberous 

 rootstocks which perpetuate the plant vegetatively were well developed, and waited 

 only the final stages in the curing process to become the perfected vegetative structures 

 which tide this species over the unfavorable season of growth. 



On the sand bar at Myers Point, the other station where this Potamogeton thrives, 

 the life conditions are not so sharply marked by the complete withdrawal of the water 

 during the dry season, and the various stages exhibited in the transmutation from aquatic 

 to land forms were easily observed. In water about 10 inches deep the continuously 

 submerged plants developed low bushy stems, with a few coriaceous leaves at the top. 

 In shallower water the plants behaved in the same way, producing bushy, stunted- 

 looking stems, which finally graded into land form with leaves in tufts or rosettes resting 

 on the exposed surface of the sand bar. The rootstocks, which were twisted and con- 

 torted in their effort to become established in the pebbly and gravelly sand bar, were 

 buried from 2 to 4 inches beneath the surface in the rich, black soil of the bar. All 

 of the intemodes of these subterranean stems were more or less thickened and often 

 attained a length of 8 to 14 inches. 



No fruiting plants were found, and this observation is in accordance with the 

 generally accepted opinion that this form of heterophyUus is propagated entirely by 

 vegetative means. Observations on the artificial propagation of this species are recorded 

 in a later chapter of this paper. 



POTAMOGETON PERFOLIATUS. 



The leaves of this plant afford valuable forage material, though the season of 

 growth is comparatively short, the plants appearing late in the spring and dying quite 

 early in the autumn. In the environs of Ithaca this species flourishes in quiet waters 

 either in a substratum of sand at the relatively shallow depths of 2 to 3 feet, or in 

 "aquatic meadows" in a substratum of mud at depths of 3 to 5 feet. The observ-a- 

 tions of Pieters (1901), in "The Plants of Lake Clair," and of Thompson (1897), in 

 "The Biological Examination of Lake Michigan" extend the range of depth at which 

 this species exists to 12 feet. During the growing season the vigorous underground 

 stems increase rapidly the output of forage material, since a single subterranean system 

 produces a large number of erect, much branched, leafy stems. The experiments of 

 Pond (1903) and Sauvageau (1894) and the observations of R. B. Thompson (1913) 

 afford evidence of other means whereby the rapid extension of this plant takes place. 

 In accordance with their observations, young branches, which are easily detachable, 

 float away and rapidly become new centers of growth. In winter the vigorous and 

 abundant subterranean system decays, leaving only the terminal shoots of two or 

 three nodes (Fryer, 1900) to continue the plant the following spring. This plant, 

 therefore, has three important means of vegetative propagation: By readily detached 

 leafy stems, and by extensions of the subterranean system, both of which operate to 

 multiply the plants during the growing season; and by the terminal portions of root- 

 stocks which, remaining in a quiescent state during the winter, establish new plants 

 in the spring. 



