70 MINNESOTA BOTANICAL STUDIES. 



The cotyledons are petiolate, the blade being ovate-oblong, 

 about 5 mm. in length and 4 mm. broad. The petiole is about 

 3 mm. long. There is but little increase in size as the plant 

 grows older. 



The first two leaves are opposite, lanceolate, short-petiolate, 

 of willow-like shape. They are about 10 mm. long before the 

 epicotyl has developed at all and do not afterward increase in 

 size. The hypocotyl is 10-15 mm. long; the epicotyl reaches 

 a length of 8 or 10 mm. 



The third and fourth leaves are nearly opposite ; later ones 

 are alternate. The later leaves become broader and longer 

 petioled, gradually assuming the deltoid form characteristic of 

 the species. 



ULMACE^. 



Ulmus americana Linn. 



The " white elm " is a native of the eastern and central United 

 States. The seeds ripen in early spring and must be sown at 

 once. They germinate in about a week. Often, but not al- 

 ways, the pericarp is carried up by the growing seedling. 



The cotyledons are at first obovate, slightly auriculate, 5 mm. 

 long and 2-3 mm. broad. They are indistinctly reticulately 

 veined. They increase but slightly in size and seldom become 

 more than 7 mm. long. They are short-petioled. The hypo- 

 cotyl is slender, not enlarged at the base, 25-35 mm. long, 

 but in time it may reach a length of 50 mm. The epicotyl is 

 about 10 mm. in length. 



The leaves are petiolate, ovate, coarsely serrate, with distinct 

 veining. The first two are opposite, the third and fourth nearly 

 so. Later leaves are alternate. 



Ulmus fulva Michx. 



The " slippery elm," like the previously described species, 

 ripens its seeds early in the spring. These, when planted at 

 once, germinate in about two weeks. The seedling resembles 

 that of U. Americana in all essential respects. 



Celtis occidentalis Linn. 



This is a fine tree native to the central United States and 

 Canada. It is known as the "hackberry." The seeds germi- 

 nate in from four to six weeks. The seed coat remains under 

 ground. 



