196 TREE ANCESTORS 



and telegraph lines, carriage hubs and similar turnery, tree nails, 

 etc. It is also valued for fuel and construction purposes, but does 

 not enter largely into the general lumber industry because of the 

 scattered supply and its special uses. 



A tree that has been cultivated for so long a time has naturally 

 given rise to numerous horticultural varieties of the parks and 

 gardens. There are also 6 or 7 additional species of Robinia, all 

 confined to North America and very similar to the preceding except 

 that they are smaller trees or even shrubs. The only one of these 

 that is generally kno^vn is the clammy locust, Robinia viscosa Vent., 

 which may be readily distinguished by the lack of fragrance of 

 its blossoms. It is a native of the mountains from southwestern 

 Virginia to Georgia, but has been extensively planted in all tem- 

 perate countries where the climate is not prohibitive and has be- 

 come extensively naturalized east of the Mississippi as far north 

 as Massachusetts. 



The rose acacia, Robinia hispida Linn, of the southern Appa- 

 lachians, a shrub with pink or purple non-fragrant blossoms; and 

 the New Mexican locust, Robinia neo-mexicana Gray, a shrub or 

 small tree of the mountain valleys of Colorado, New Mexico, 

 Arizona, and southern Utah, with handsome blossoms, are both 

 favorites outside their natural limits for ornamental planting in 

 both this country and western Europe. 



The geological history of the locust is beset with difficulties, 

 the leaflets usually becoming detached before fossilization and 

 both leaflets and pods being often impossible to differentiate 

 from other and unrelated leguminous leaflets and pods. Tliis 

 difficulty of distinguishing between the fossil leaflets of the various 

 genera of Leguminosa^ has led paleobotanists to estabhsh a purely 

 formgenus known as Leguminosites for leaflets of this sort that 

 cannot be identified with certainty beyond that they are legumi- 

 nous. Large numbers of species of Leguminosites ranging in age 

 from the Upper Cretaceous through the Tertiary are known. 

 Among these are several that might well represent an Upper Cre- 

 taceous locust, but such an identity is not conclusive. Certain 

 pods from the top of the Cretaceous in Colorado have been referred 



