46 EASY LESSONS IN VEGETABLE BIOLOGY. 



CHAPTER VIII. 



THALLOGENS, OR DIVISION OF LABOR IN PLANTS. 



1. IN the plants which we have been considering 

 each cell is an individual, but in all other kinds the 

 plant, or individual, is made up of many cells, each 

 one of which has a special work to do. Some belong 

 to the root, some to the axis, or stem, and others to 

 the leaves, flowers, or seeds. In the type of Thai- 

 logens there is no very accurate division of root, stem, 

 leaves, and flowers, and the whole plant is called a 

 thallus, a frond, or green expansion. Under this 

 type we find the classes of Algce, or Sea-weeds; 

 Lichens, or the dry, leafy, or mossy patches on trees, 

 stones, etc. ; and Fungi, or mushrooms, molds, and 

 their allies. 



2. The Algce, or Sea-weeds, have been divided 

 into three orders, the Red, the Olive, and the Green 

 sea-w r eeds. In the more complicate forms we find a > 

 sort of distinction of root, stem, and leaf, which re- 

 minds us of still higher plants, but the distinction is 

 more apparent than real, since the root and stem 

 serve little other use than the mere mechanical at- 

 tachment of the plant. The whole plant is made up 

 of cells, and there are no proper vessels. Chap. VI, 



