Seydel. who has made investigations along this line arrived at these figures* 



Temp, in Oxygen in 



centigrade can per liter 



In thick growths of reeds 1A.7 2,979 



In loose Glyceria growth 16.8 5«974 



In clear water 17.2 5.716 



Betireen frog lettuce 17.3 7.739 



Above water thyme 17.2 8.503 



An excessive growth of submerged plants ivill become noxious, of course, especially 

 with the development of large floating leaves, since this vrLll shade the deeper layers of 

 water, thus making the discovery of food more difficult for the fish. 



Also, an excessive growth of sutmerged flora leads easily to an extremely high oxygen 

 rate, to strong biogenic decalcification and to a pH rate increase, especially during clear 

 daj's, factors viiich in turn may produce sickness among fish, especially gas bubble disease 

 among the brood stock (fin rot, etc.). 



It has also to be kept in mind tliat plants, during darkness, consume but do not produce 

 oxygen. A thick growth of plants vail therefore reduce the oxygen rate of a pond dui'lng the 

 hours of the night. The minimum is always reached at daybreak. 



i!any submerged plants are lacking in roots and even root-bearing plants use them chief- 

 ly only for support (exceptions are the v/ater lilies). As far as is known today, water 

 plants receive all of their nounshment — for example, alkaline and phosphoric acid combin- 

 ations — through the whole surface of their epidermis. Tliis also explains that the develop- 

 ment of a submerged flora depends almost entirely upon the nutrient contents of the water. 

 (P. Schemenz, 1927). Their very presence in ponds is thus characteristic. 



The most commcm and at the same time most serviceable submerged plants — characteristic 

 for productive waters — are the different Potamogeton and Uyrl ophyllum species, also El ode a 

 canadensis . Ranunculus aquatilis and Polygonum amphibium . 



EL odea, according to Ruttner, ranks first as to assimilating performance, hence of 

 groT/th, and is at the same time most productive in oxygen. 



Next in line come Potamogeton praelongus . Chara foetida. Spirogyra. hanun cuius and 

 Ljyriophyllum . 



Their needs with regard to v;atei-, soil, light and warmth are little known; on the other 

 hand, we also find quite often different Chara ceae species in ponds and their needs are some- 

 what better knovjn, thanks to recent investigations by Stroede . 



He found that all Chara ceas species adapt themselves readily to chemical factors 

 (thermic influences, draining, etc.), and he classified them^ — in regard to salt contents 

 of v.-ater — into sweet water, brackish water and seawater species. Uost common in ponds is 

 Chara fragilis ( HiteHa syncarpa ? ) . and irtiich adapts itself to low as well as to very high 

 calcium contents, provided tliat the pH rate does not fall belov; 6.5. 



The Fontinalis species are more rare in ponds but peat moss ( Sphagnum species) will 

 cover the floor of ponds in enormous quantities, regardless of low or very high calcium 

 rates. 



nasturtium. Veronica beccabunga — partly surface plants — and also the Callitricheae 

 species may be regarded as "conductor plants" for good and productive trout ponds. 



43 



