Dec, 1905.] Free-floating Plants of Ohio. 421 



species like Azolla develop anthocyan while others like Salvinia 

 are protected by hairs. In some, as in Lemna trisulca the 

 chlorophyll granules shift their position with the changes in the 

 intensity of the light. In diffused light the granules lie against 

 the horizontal walls, but if strong light strikes the surface 

 perpendicularly they are transferred to the vertical walls. 



Vegetative propagation is usually effected with great rapidity 

 by the branching and budding of the stem and the separation of 

 these branches. The duckweeds and other free-floating plants 

 frequently cover great areas very closely and largely prevent 

 the formation of waves when one throws a stone into the water. 

 In the south the water hyacinth (Piaropus crassipes (Mart.) 

 Britt.) covers large areas of rivers and lakes, causing much 

 inconvenience to navigation. 



Among the Ohio plants which may be found floating free in 

 the water though normally attached may be mentioned the fol- 

 lowing: Hottonia inflata Ell., Philotria canadensis (Mx.) Britt., 

 Ceratophyllum demersiim L., Myriophyllum sp.. Utricularia sp., 

 and Potamogeton sp. 



Utricularia has little bladders which not only assist in float- 

 ing the plant but act as traps for capturing small organisms 

 which are digested for food. 



The typical, free-floating plants which are found in the 

 secondary plankton of Ohio are as follows: 



LIVERWORTS. 



Riccia fluitans L. 



Ricciocarpus natans (L.) Corda. 



WATER FERNS. 



Salvinia natans (L.) Hoffm. 

 Azolla caroliniana Willd. 



MONOCOTYLS. 



Spirodela polyrhiza (L.) Schl. 



Lemna trisulca L. 



Lemna cyclostasa (Ell.) Chev. 



Lemna minor L. 



Wolffia Columbiana Karst. 



Wolffia punctata Griseb. 



