6 ELEMENTARY STUDIES IN BOTANY 



very different, they do the same kinds of work. The 

 work does not become more complex, but the structures 

 developed to do it become more complex. 



It is believed that the simple plants were the first mem- 

 bers of the plant kingdom, and that plants gradually be- 

 came more and more complex until the structure of our 

 highest plants was reached. To understand the structure 

 of the higher plants, it is necessary, therefore, to approach 

 it as plants approached it, by beginning with simple forms 

 and noting the appearance of one change after another 

 until the greatest complexity is reached. It happens that 

 the plants we use most are most complex, and therefore 

 the tendency has been to study them first and often to 

 study them only; but we are assuming in this book that 

 a study of plants is intended to develop some real knowl- 

 edge of plants. 



Therefore, in the following pages we will begin with the 

 simplest plants, and discover how the plant kingdom gradu- 

 ally became what it is. In this way we shall really know 

 something of the structure and work of the plants we use 

 most. 



7. The four great groups. It is customary to divide 

 the plant kingdom into four great groups. These groups 

 proceed from the simplest to the most complex plants, 

 so that it will be helpful to obtain a glimpse of them in 

 advance, as this will explain the order in which the plants 

 are presented. 



(1) Thallophytes. These are the simplest plants, and 

 therefore the lowest group. The name means "thallus- 

 plants," and a thallus is a simple kind of plant body which 

 will be understood when it is met. The conspicuous mem- 

 bers of this group are called Algae and Fungi, the former 

 being the " seaweeds/' although many of them live in 

 fresh water, and the latter including such forms as mush- 

 rooms among their higher members. 



