226 



IMPORTANT FAMILIES OF PLANTS 



shell bark, and H. olivoeformis, H. pecan, the pecan of com- 

 merce) are well known for their nuts and useful woods. 



Propagation. The members of this family can be grown 

 from seeds or by grafting. The fact that seedlings are subject 

 to more or less variation makes it necessary to perpetuate de- 

 sirable varieties by grafting, which must be done with consid- 

 erable care in order to be successful. 



FIG. 148. Pecan nuts, showing one of the many forms grown for market. (U. S. D. A.) 



OAK FAMILY 



This family is similar to the preceding. The flowers are 

 monoecious. The staminate flowers in catkins, calyx five-parted 

 (occasionally five to twelve), stamens two to twenty. The pis- 

 tillate flowers terminal, six-parted, and attached to the two- to 

 seven-chambered ovary. Fruit a one-seeded nut. This family 

 includes the oaks, chestnut, hazelnuts, beech, and others. 



There are many species of oaks (Quercus) which are among 



