248 



FIRST YEAR SCIENCE 



the Russian thistle which was introduced into this country 

 in 1873 and which has now become a national pest. 



115. Life of the Sea. The plants living in the sea are 

 nearly all of a low order. The mangrove trees which 

 border some tropical shores represent their highest type. 

 The most abundant of sea plants, the seaweeds, have no 



DIFFERENT KINDS OF SEAWEED. 



flower or seed or true root, although most of them have 

 an anchoring device by which they are attached to the 

 bottom. Their food is absorbed from the surrounding 

 water. They have developed little supporting tissue, but 

 instead have bladder-like air cavities or floats, which 

 enable them to maintain an erect position or to float freely 

 in the water. Usually they abound near the shore where 

 the water is shallow. 



The vast surface of the open sea supports few plants 



