POTAMOGETONS IN RELATION TO POND CULTURE. 267 



grew in banks in sand and silt bottoms at a depth of 5 to 7 feet. They were quite 

 unmixed with other aquatics. In July and early August the long heavily fruited 

 spikes floated in dense masses at the surface and gave to these areas of the water a 

 characteristic brown look. Proliferations were not found on these plants during the 

 summer; fruits, however, were more abundant than on any other form of pectinatus. 



The gigantic form of pectinatus grows in deep water. Plants 8 feet long are com- 

 mon, although many average but 5 feet at the end of the growing season. This form 

 grows in a substratum of sand and silt at depths varying from 6 to 1 2 feet in a region 

 of the lake exposed to a more or less constant sweep of the wind. The plants, there- 

 fore, which grow practically to the surface of the water, are subjected at times to 

 vigorous wave action. Altogether these environmental conditions favor a growth of 

 remarkable luxuriance. The plants grow in banks, and so thickly as to preclude the 

 possibility of encroachment by other forms of vegetation, though in shallow places, 

 where the growth becomes sparser, a few scattered representatives of P. crispus, 

 P. perfoliatus, and Heteranthera duhia occur. 



This form of pectinatus begins growth early in the spring. In May, 1913, the 

 plants already approached the surface of the water. On June 21, 1913, a plant bearing 

 a single floral spike was found, although in several collections made thereafter neither 

 flower nor fruit was obtained. This appears to be the first record of a floral spike on 

 this form of pectinatus. From the collections made in November a few tubers were 

 found on the tips of the foliage sprays of the plants that were uprooted from their 

 natural moorings, although they were found more commonly on sprays that were floating 

 in the drift. This latter observation is an agreement with Dudley (1886), who observed 

 and described this form in Lake Cayuga. No rootstocks were secured, since attempts 

 to uproot the plants at such depths with a grapple resulted always in breaking the 

 stem just short of the subterranean system. This appeared to be embedded firmly and 

 deeply in the substratum, at least more deeply than the length of the grapple teeth, 

 which measured 4 inches. However, the bases of the erect stems, the parts which 

 develop just above the rootstocks, possessed remarkable examples of proliferation. 

 Thickened runners, more or less contorted, arose from leaf axils at the bases of the 

 erect stems (fig. 50, A), terminated by large, elongate tubers. The bases of the stems 

 were hard and woody, more especially so in the regions where they became detached 

 from the underground system. This condition suggests a continuation of the woody 

 structure in the subterranean parts. It may be inferred perhaps, from the general 

 habit of the plant and the attendant conditions of growth, that the rootstocks are per- 

 ennial, and that the basal runners, which bear in abundance large tubers and green 

 shoots, are the chief propagative structures of this form of pectinatus. 



POTAMOGETON ROBBINSII. 



Although this Potamogeton is less well known than the other species, it is 

 destined to be regarded as an important aquatic forage plant, first, because it is very 

 proHfic, and, second, because the foliage is very generally eaten. The habitat of this 

 species, where it has been under observation, is not unlike that of P. amplifolius, with 

 which it is often found in association. It has been observed in the quiet waters of lakes 

 and ponds at depths of 3 to 5 feet in a substratum of rich, black mud. The stems 

 ascend from a somewhat creeping base and branch profusely in a more or less two- 



