(i(i 



NATURE STUDY 



IX SCHOOLS. 



It will hud or divide and so will start a new colony of coral polyps. Pretty 

 soon the colony begins to take the shape of a head. The little polyps on 

 the side grow much better than those on the top, as they can get more of the 

 food. The polyps in the center grow weaker and smaller than those on the 

 outside, causing the head to become flattened. Mud and debris now settle 

 upon the head, killing the polyps beneath. As the polyps on the sides keep 

 building up all the time, and the polyps in the middle die. the colony 

 forms a cup shape. The side polyps build up and sidewise more and more, 

 and the mud settles in the middle so the hollow cup grows larger and 

 deeper. Alter many, many years, in this way the coral polyps reach the 

 top of the water, making the coral island in the shape of a ring, called 

 an atoll. An atoll in a perfect ring has never been found; there is always 

 a break in it somewhere, and often more than one. The water inside of 

 the atoll is called a lagoon, and as the water is very calm, it is an ex- 

 cellent harbor for ships during storms. 



The coral island has now no earth or vegetation on it. but the man- 

 grove, a certain kind of tree, can thrive here without earth, as it grows in 



Fig. 30. 



Mangrove fruit, by Beatrice Hodges. A, entire fruit; B, base; C, folded leaves: D, rootlets. 



salt water. In the spring, the mangrove buds, and later on. these buds pro- 

 ject a long cigar-shaped fruit. As the fruit gets ripe, this cigar-shaped part 

 drops into the water. There are little leaves on the top of this and some 

 roots on the bottom. Before the long part dropped off, the leaves were 

 folded in the cup-shaped bud. As the heavy part of the bud or fruit is 

 in the lower part of this cigar-shaped part, it floats with the leaves up. As 

 it is in the spring the water is calm and the bud floats along very smooth- 

 ly. 



