374 Annals of the Carnegie Museum. 



I 



The CastaUa-Nymph(Ba Formation. 



The water lily zone {^Castalia-Nymphcea formation) is almost as 

 regularly present in the small ponds and lakes of the glaciated region 

 of the northern states as is the Potamogeton formation. It occupies 

 water, usually between the depths of one and one-half and six feet, 

 where the bottom is covered to a depth of often several inches with a 

 black mud composed very largely of humus. In the Chimney Ponds 

 the formation consists of the following species : 



Fades. — 



Castalia tuberosa, NymphcBa advena. 



Principal Species. — 



Pontederia cor data. 

 Secondary Species. — 



Sagittaria latifolia, Potamogeton nutans, 



Naias flexilis, Myriophyllum spicatum, 



Lemna minor, Utricularia vulgaris, 



Philotria canade?isis. 



There is a strong tendency towards zonation in this structure. 

 Wherever Castalia appears it prefers the deeper part of the habitat, 

 thus forming the Castalia consocies, with which are usually associated 

 some of the Potamogetons — notably P. natans, and often Naias and 

 Myriophyllum . 



The outer (shoreward) part of the formation is characterized by 

 Nytnphcea advena, forming thus the Nyniphcea advena consocies, with 

 which is associated Pontederia cordata, which during early and middle 

 summer becomes prominent in beautiful clumps (families and communi- 

 ties), characterizing thus the Pontederia cordata aspect. Other 

 species in this consocies are Sagittaria latifolia, Lemna minor, Utricu- 

 laria vulgaris, and scattering individuals of the other secondary species 

 of the consocies. 



The Castalia-Nymphaa formation probably builds up the soil more 

 rapidly than does any other formation in the pond. The rhizomes of 

 the characteristic plants are for the most part quite large, and both 

 when alive and when decayed contribute quite considerably to the in- 

 crease of the soil substratum. Furthermore the tangle of fine-leaved 

 submerged vegetation together with the long petioles and broad leaves 

 of the water-lilies brings about a freedom from water-currents, and 

 makes more certain the deposition within the limits of the zone of its 

 abundant annual accumulation of vegetable debris. 



