24 AQUATIC PLANTS IN POND CULTURE. 
observations in the ponds here described. His application of the 
fact to fish culture, however, it would seem might be put differently. 
While it is true that good soil is to be sought, it should be added 
that for very rich soil it is important to avoid, if possible, plants 
with a tendency to rankness. 
The quality of the water is a factor which may entirely control 
the conditions of fish culture. At Cold Springs, Ga., where the 
water is soft, it is impossible to obtain a permanent growth of vegeta- 
tion, and the ponds must accordingly be restocked from time to time. 
Two species of Myriophyllum are the only plants that have been 
successfully maintained through a season. It sometimes happens 
also that even with exuberant vegetation there is a dearth of animal 
life, and this might be ascribed to some property or deficiency of the 
water, just as is the abundance of certain amphipods and other crus- 
taceans which are an important food for young fish, these forms being 
known to thrive and multiply best in water containing lime. 
A further quotation from Doctor Pond, in reference to Cerato- 
phyllum, is of interest in this connection. This nonrooted plant 
he shows to be dependent primarily upon the nutrient salts in solution 
in the water, and thus a competitor of many of the small forms of 
life, which derive their sustenance from the same source. A pond 
filled with Ceratophyllum therefore would be expected to contain 
less of these forms and, consequently, of the forms that live upon 
them. From this it would seem to follow that the water best suited 
to Ceratophyllum would not contain sufficient food for young fish 
if that plant were the predominant species, and if this reasoning 
is correct the value of Ceratophyllum would depend upon the pres- 
ence of sufficient rooted vegetation to offset the effects of competi- 
tion. Such may have been the conditions at the Fish Lakes, where 
there were an unusually large number of species of rooted plants, 
above all of which, however, the superintendent believed Cera- 
tophyllum the best. 
No particular species of aquatic plant can be said to be always de- 
sirable. The endless interrelations of plant and animal life and 
physical surroundings make the problem a special one for each locality. 
It should be noted, however, that according to the data here presented 
great caution should be used as to the introduction of the pondweeds, 
waterweed, water clover, water-lilies, frogsbit, and cattail. The last 
two can not be regarded as desirable in any fish pond. Chara, in- 
digenous at some stations, is in most cases so much in favor as a food 
producer that notwithstanding its objectionable characters it is con- 
sidered the best plant for fish-cultural purposes. It should be borne 
in mind, however, that at the stations where this plant is a favorite 
the ponds are of more recent construction than at Wytheville, for in- 
stance, where Chara is especially troublesome. 
