3i6 



ELEMENTARY BIOLOGY 



370. Protection of seed. As living things seeds are exposed 

 to destruction by other plants or by animals and to injury 

 by inorganic factors of the environment, as excessive low tem- 

 perature and excessive moisture or drought. We find many 

 fruits covered with spines ; others have hard or tough cover- 

 ings or shells ; still others contain bitter or acrid substances. 





Fig. i4_i. Dehiscent fruit 



Seeds are scattered by the opening of the fruit in a definite way. /. chestnut ; 2, witch 

 hazel ; .,'•, poppy ; 4, pea ; 5, monkshood 



Seeds that become separated from the fruit are frequently 

 tough-skinned or covered with some other protective layers 

 (see Figs. 7 and 143). 



371. Escape of seeds. The seed attached to the parent 

 plant and surrounded by other structures is of no significance 

 in the life of the species. To be in a position to perform its 

 functions, the seed must ^^/ out and ^^/ azvaf — and the 

 farther away the better, in most cases. 



Many common seeds escape from the parent plant through 

 the splitting open of the ripe fruit along definite lines or by 



