288 TEXTBOOK OF BOTANY 



fruits and seeds. Their effect is seen in the distribution of 

 species of plants, sometimes through long distances, along the 

 shores of rivers and lakes, as well as along sea-coasts and from 

 island to island in the seas and oceans. The coconut palm 

 grows on tropical coasts, especially on coral islands, and its 

 distribution depends very largely upon the carrying of its 

 fruits from place to place by ocean currents. 



Many different means are resorted to by plants to secure 

 the scattering of their seeds by animals. The fruits of a 

 good many common weeds have hook-like or barb-like attach- 

 ments by means of which they cling to the 

 coats of animals or to the clothing of 

 human beings that brush against the 

 plants on which they are borne. Some of 

 these hook-like attachments, such as those 

 of stick- tights and beggar-ticks, are out- 

 growths from the fruit coat ; those of bur- 

 dock burs and cockle-burs develop from 

 Fig. i68. — Ripe bracts just below the flower cluster. The 



fmit^ of a lily, be- ^j^g distribution of the seeds of many 

 ginning to split at . -^ 



the top. plants IS due to the fact that their fruits 



or parts of their fruits are edible. An 



animal that eats such a fruit is of course likely to swallow 



the seeds also ; but the latter are usually (though not 



always) protected by their seed coats from the digestive 



juices of the animal, and so pass uninjured through its 



alimentary tract and may be deposited a long way from 



the place where they were produced. While they are 



growing, and the seed coats are still soft and thin, the fruits 



that are later to be edible are usually hard and sour or bitter ; 



it is only when they are ripe and the seed coats are fully 



formed that they are pleasant to eat. These edible fruits are 



of special interest to us. Among them are the stone fruits 



(cherries, plums, apricots, and peaches), gourd fruits (such 



as the pumpkin, squash, cucumber, and melons), citrus fruits 



