Nov., 1902 .] Ohio Plants with Dissected Leaves. 315 
light, differences in nutrition, temperature, and so forth, which is 
the commonly accepted explanation for the form of submerged 
leaves. This explanation, however, is too general to be entirely 
satisfactory. In tins connection, McCallum* has been conducting 
experiment with Proserpinaca pal 11st r is, at the Hull Botanical 
Laboratory. These experiments seem to indicate that the hereto- 
fore accepted explanation based upon diminished light, nutrition, 
and so forth, will not hold good. It appears that the only constant 
factor in all cases where the water form develops is the checking 
of transpiration and the increased amount of water in the proto- 
plasm. Whatever the inciting cause may be, it seems that this 
condition brings out a certain set of hereditary characters while 
the absence of it produces a different set ; just as a root in the soil 
is a typical root, but when growing above the ground may some- 
times produce buds and leaves. 
IN WATER. 
Ceratophyllum demersum — in ponds and slow streams. 
Ranunculus delphinifolius — in ponds. 
Batrachium tricophyllum — in ponds and streams. 
Batracliium divaricatuin — in streams. 
Roripa Americana — in lakes and slow streams. 
Podostemon ceratophyllum— in shallow streams. 
Floerkea proserpinacoides— in marshes and along rivers. 
Proserpinaca palustris — in swamps. 
Myriophyllum spicatum— in deep water. 
Myriophyllum verticillatum— in both deep and shallow water. 
Myriophyllum tenellum — on sandy bottoms of ponds and streams. 
Myriophyllum heteropliyllum — in ponds. 
Conioselinum Cliinense — in cold swamps. 
Hottonia itiflata — in shallow stagnant ponds. 
Utricularia vulgaris — in brooks and ponds. 
I'tricularia intermedia — in shallow water along margins of pools and 
ponds. 
I'tricularia minor — in shallow ponds and bogs. 
Utricularia gibba — in shallow water or in mud on borders of ponds and 
pools. 
Bidens Beckii — in ponds and streams. 
ON DRY LAND. 
Delphinium consolida— in waste places. 
Delphinium Carolinianum — on prairies and open grounds. 
Bieuculla cucullaria — in woods. 
Bicuculla Canadensis — in rich woods. 
Capnoides flavulum— in rocky woods. 
W. B. McCallum. On the Nature of the Stimulus causing the Change of Form and 
Structure in Proserpinaca palustris. Dot. Gaz.j,/: 93-10S, 1902. 
