Linnaeus' description seems to have thoroughly confused all of the earlier botanists. They were in doubt, first, as to what species was intended for Vulpina; second, as to the distinguishing characters between Riparia and Cordifolia. Gray classed Riparia as a variety of Cordifolia. Engelmann was the first to draw attention to the specific characters which separated these two sorts and these he gives as follows: 1st. Riparia has thin diaphragms, Cordifolia thick. 2d. Riparia blooms early, Cordifolia late. 3d. Riparia propagates readily from cuttings, Cordifolia only with difficulty. 4th. Seeds of the Riparia have indistinct or almost indistinct, depressed chalaza and raphe, while the chalaza and raphe of the Cordifolia seeds are elevated and distinct. To these Bush[137] added the further distinguishing character that on the shoots the small terminal leaves of the Cordifolia open as soon as formed, while those of Riparia remain folded for some days after they are formed, become larger and then expand gradually. Riparia is the most widely distributed of any American species of grape. It has been found in parts of Canada north of Quebec and from thence southward to the Gulf of Mexico. It is found from the Atlantic coast westward, most botanists say to the Rocky Mountains, but Munson gives the western limit as Salt Lake. Since Munson is more familiar with the district lying west of the Rocky Mountains than any other botanist who has paid attention to grapes, he is probably correct. Usually it is found on river banks, on islands or in upland ravines. Riparia has always been considered of great promise in the evolution of American grapes. It can hardly be said that it has fulfilled expectations, there probably being no pure variety of this species of more than local importance, and the results of hybridizing it with other species have not been wholly successful. The reason why attention was early turned to Riparia was because of the qualities presented by the vine rather than those of the fruit, particularly its hardiness and vigor. However, both of these qualities are quite variable, and it is only reasonable to suppose that in such a widely distributed species, plants found in a certain region would have adapted themselves to the conditions there present; thus it should be expected that the northern plants would be more hardy than those from the South and the western prairie forms more capable of resisting drouth than those from humid regions; this is found to be the case. It is consequently impossible to say what conditions best suit this species; it may be said, however, that it is adapted to a great variety of soils and locations; Riparia vines, or certain ones of them, have withstood a temperature of 40 to 60 degrees below zero and they show equal ability in withstanding the injurious effects of high temperatures in the summer. On account of its habit of early blooming, the blossoms sometimes suffer from late frosts in the spring.