149 



THE ELMS— ULMUS (Tourn.) Linnaeus. 



The members of this genus are usually trees, rarely shrubs. About 

 15 species are known of which number 6 species are native to North 

 America and 2 to the State of Pennsylvania. 



The leaves are simple, alternate, two-ranked, straight-veined, and 

 unequal-based. The flowers may appear before or after the leaves. 

 The 2 species native to this State produce their flowers early in 

 spring before the leaves. The fruit of the native species ripens in 

 spring shortly after the flowers have matured. It consists of a flat 

 seed surrounded by a thin papery wing. 



The trees yield valuable wood and some of them also produce a 

 tough inner bark which is used for food, in medicine, and manu- 

 factured into ropes and coarse cloth. The Elms are not only val- 

 uable commercially but also attractive ornamentally. The native 

 American Elm and the introduced English Elm (Ulmus campestris 

 L.) are not only beautiful in summer when covered with a dense 

 foliage but also in winter when the little twigs and branches, and 

 the massive trunk and limbs stand out against the sky. The sub- 

 joined key will aid in distinguishing the two native species of Elm 

 and the commonly introduced English Elm: 



SUMMER KEY TO THE SPECIES. 



Page. 



1. Leaves smooth above or nearly so; fruit ovate or oval, ciliate on margin; flowers on 



slender drooping stalks, TJ, americana 151 



1. Leaves very rough above; fruit circular, not ciliate; flowers nearly sessile, 2 



2. Small to medium-sized native tree; inner bark mucilaginous; branchlets and pedicels 



downy; fruit densely brown-hairy over seed IT. fulva 150 



2. Large introduced tree; inner bark not mucilaginous; branchlets and pedicels smooth; 



fruit smooth throughout, TJ. campestris 149 



WINTER KEY TO THE SPECIES. 



1. Bud-scales densely brown-hairy; inner bark mucilaginous; twigs grayish and rough, 



U. fulva 150 



1. Bud-scales not densely brown-hairy; inner bark not mucilaginous; twigs not grayish 



nor rough, 2 



2. Buds chestnut-brown; bud-scales with darker margin; bark ridged; twigs without 



corky ridges; form of the tree decidedly deliquescent, U.americana 151 



2. Buds smoky-brown to almost black; bud-scales rather uniform in color; bark rather 

 firm, often roughened into oblong blocks; form of tree intermediate with an excur- 

 rent tendency XT. campestris 149 



