SEXUAL REPRODUCTION. 225 



tective coverings have been completed. The devices by 

 which seeds are scattered are dependent upon the number and 

 character of the seeds and the nature of the pericarp. Plants 

 adapt themselves so as to employ as distributing agents wind, 

 water, and animals, or they develop special mechanisms for 

 casting off the seed as a projectile. A consideration of these 

 adaptations belongs to ecology. (See Chap. XXVI.) 



312. Renewed growth. — After a time, if the seeds become 

 wet and are kept at a suitable temperature, with a supply of 

 air, the embryo resuriies its growth, i.e., the seed "germi- 

 nates. ' ' This growth soon bursts the seed coats ; the food is 

 digested and absorbed ; the young plant sends its roots into 

 the soil and its leaves to the light, and by the time the food 

 store is exhausted, is ready to make its own living. 



313. Summary. — Sexual reproduction consists in the 

 union of a male cell and a female cell (neither able to grow 

 further) to form a single new cell capable of growing into a 

 new plant. The processes and organs are not described here. 

 The direct result is the formation of a " resting spore ' ' which 

 remains dormant for a time ; or else the immediate develop- 

 ment of an embryo plant. In the latter case the embryo, in 

 all but seed plants, continues its growth, interrupted only by 

 external conditions, until it becomes a full-grown plant. In 

 the seed plant it becomes dormant while still small. Before 

 its growth is interrupted, its development has induced the 

 growth of the ovule, in which it lies, until the two form the 

 ripe seed. Adjacent parts also grow and with the seed con- 

 stitute the fruit. The changes in the growing parts produce 

 dry, fleshy, accessory, or multiple fruits. The seeds are finally 

 scattered by various ingenious devices. With a suitable sup- 

 ply of heat, air, and water, the embryo resumes its growth 

 and continues to grow until it forms a mature plant. 



