164 



THE ROSE FAMILY ROSACEAE. 



This is one of the largest families of plants. It comprises about 

 100 genera with about 1,500 species, many representatives of which 

 are native to North America. The flora of Pennsylvania comprises 

 about 30 genera with more than 100 species. 



The members of this family comprise trees, shrubs, and herbs. 

 They have a world-wide distribution. A few of the trees are impor- 

 tant on account of the timber w r hich they produce while many are 

 important on account of the valuable fruit which they yield. Most 

 of our common and well-known fruit trees belong to this family. 

 Many of its shrubs are common and most attractive. 



The leaves of the representatives of this family are simple or com- 

 pound and always alternate, never opposite. The flowers are per- 

 fect, showy, and open in spring or early summer. Many species have 

 very fragrant and attractive flowers. The fruit 'matures in one sea- 

 son and is variable in form and structure. It may be in the form of 

 achenes, follicles, pomes, or drupes. /Some species like the Cherries, 

 Plums, and Peaches have fruits which are edible and well known. 

 Their pulp is usually juicy, sweet or bitter, sometimes astringent, 

 and covers a hard-shelled round or flat seed. On account of the 

 palatable nature of most of the fruits they are readily eaten by man, 

 birds, and wild animals. The seeds are not injured by passing 

 through the alimentary canal of animals and hence may be thus 

 widely dispersed. The wood in many species is valuable but in our 

 flora all but one species remain too small to be of any commercial 

 value. 



Of the large number of genera and species found in Pennsylvania 

 only 9 species belonging to 4 different genera are described below. 

 In addition to these a few other genera have well-known representa- 

 tives. The Ninebark (Physocarpus opulifolius, (L.) Maxim.), is a 

 common shrub throughout the State along rocky banks of streams. 

 It is the only representative of its genus in Pennsylvania. The 

 Strawberries belonging to the genus Fragaria have a few common 

 representatives. The Raspberries, Blackberries, and Dewberries, be- 

 longing to the genus Rubus, have about 20 species native to this 

 State. The Wild Roses, belonging to the genus Rosa, have at least 

 7 species native to the State. In addition to these there are many 

 herbaceous species. 



KEY TO THE GENERA. 



Page. 

 1. Unbranched thorns pjesent on twigs, situate at the- nodes, Crataegus 170 



1. Thorns not present on twigs 2 



2. Fruit a drupe; pistil one; twig with characteristic taste and odor, usually 



covered with horizontally-elongated lenticels, Prunus 165 



2. Fruit a pome; pistils more than one usually 3-5; twigs with a different character- 



istic taste, without horizontally-elongated lenticels 3 



3. Cavities of the ovary same number as the styles; buds not narrow-conical and not 



g reenish-3 cllow, Pyrus 172 



3. Cavities of the ovary becoming twice the number of the styles; buds narrow-conical 



and greenish-yellow Amelanchier 174 



