140 RELATIONSHIP OF PLANTS 



ciated with outgrowths that appear as the burr in the chestnut 

 and beech and as a cup in the oak. On account of these and 

 other common characteristics these genera are supposed to be 

 related and are therefore grouped together in one family. A 

 family is composed of allied or related genera. The name of 

 the family is derived from some characteristic genus in the group. 

 In this case it happens to be the beech or Fagus. To distinguish 

 a family from a genus the termination aceae is added to the base 

 of the generic word, in this example making the family name 

 Fagaceae. So we have the three allied genera, oak, beech, and 

 chestnut forming the beech family or Fagaceae. In the same 

 way it will be found that families are related and joined to- 

 gether into a still larger group known as the order. The flowers 

 of the birch, alder, water beech, and hazel genera are very simi- 

 lar and consequently form a family known as the birch family or 

 Betulaceae, Betula being the name of the birch genus. It will 

 also be noticed that there is a similarity between the flowers of 

 the Betulaceae and Fagaceae. This relationship is expressed by 

 placing them in the same order known as the beech or Fagales, 

 the termination ales being employed to distinguish the order just 

 as aceae characterized the family. So also orders are related 

 and grouped into classes. For example, the Fagales and many 

 other orders are characterized by having seeds with two cotyle- 

 dons. Several other orders have seeds with but one cotyledon. 

 This relationship is expressed by grouping the orders into two 

 classes, Dicotyledones and Monocotyledones. In both of these 

 classes the seeds are inclosed within the pistil, but in the cone- 

 bearing trees the seeds are exposed on a flat scale-like organ. All 

 seeds producing plants belong to one or the other of these two 

 groups. So we have two subdivisions, the Angiospermae, mean- 

 ing seeds inclosed, and the Gymnospermae, meaning naked seeds. 

 If now we stop to consider still larger groups than subdivisions, 

 it will be noted that many plants do not produce seeds, as in the 

 case of the ferns and mosses, etc. So a final grouping of plants 

 into divisions or subkingdoms may be made. All seed-bearing 

 plants form the division Spermatophyta, meaning seed plants; 

 the ferns comprise the division Pteridophyta, meaning fern plants, 



