INTRODUCTION. 9 



be underrated ; but too much cannot be said against that 

 view of the science which still prevails in many schools, 

 that the sole purpose of the study of botany is to learn 

 the names of plants. 



A point of quite general agreement in the classification 

 of plants, and one that is sufficient for the beginner, is a 

 division into the four groups of ThaUopkytes, or plants 

 which have no true roots, stems, or leaves ; Bryophytes, 

 or Moss plants ; Pteridophytes, or Fern plants ; and Sper- 

 maphytes, or Seed plants. 



The Thallophytes. These plants include a very large 

 number of lowly organized forms. They are distinguished 

 from all the plants above them by the fact that they are 

 either unbranched, or are divided into branches which are 

 just alike in structure ; in other words, they show no 

 differentiation into stem, root, and leaf, though in some 

 plants there is a foreshadowing of such differentiation. 

 The plant body is called a thallus. There is a more or less 

 regular alternation of generations between forms which 

 produce simple spores and forms that produce cells which 

 unite sexually and give rise to a zygospore, or oospore, from 

 which a new plant develops, though in many of the Thal- 

 lophytes this alternation of generations is unknown, or is 

 wanting. The sexual cells are known as gametes; the 

 form of the plant which bears them is the gametophyte. 

 The form of the plant which bears simple spores is known 

 as the sporophyte. This alternation of generations between 

 gametophyte and sporophyte is by no means confined to 

 the Thallophytes. It extends in general throughout the 

 whole vegetable kingdom, and is more highly marked in 

 other groups than it is in the Thallophytes. In the case 

 of the Thallophytes, the form which bears the name is 

 usually the gametophyte, as this is the most highly devel- 

 oped form of the plant. Another fact which distinguishes 

 the Thallophytes is that the female gamete is never an 



