270 STRUCTURE AND VITAL PROCESSES OF PLANTS 



necessary for the growing seedling packed in their cotyledons, 

 which thus become swollen. The food-suhstance either contained 

 by the cotyledons or by the endosperm is also utilizrod for food 

 by man, as well as by many animals. 



AVhen the seeds are mature and their germs in a position to 

 live alone, they must leave the protecting covering (pericarp) 

 and be dispersed, so as not to germinate just under or near the 

 mother-plant where the young plants would simply suffer from 

 her shade, and from the fact that she had used up some of the 

 supplies of mineral food available, and that they would have a 

 hard struggle for life with one another. The germs or young 

 plants must, therefore, be so constructed as to be able to go on 

 a long journey without perishing. They are in this state in the 

 ripe seed. When fully formed, they cease to be watery, the 

 place formerly occupied by water being now filled with starch or 

 oil, and the seed-coat becomes hard. 



Many seeds, it is true, do not end their journey in a very 

 suitable place, but die by hundreds and thousands for want of 

 congenial surroundings, and it is for this reason that such large 

 numbers of seeds are produced. 



■ bJ How fruits allow their seeds to escape. 



In order to enable the seeds to start on their journey, the 

 fruit which had to protect them during tlie period of their growth 

 and ripening, must set them free. This is done in various ways. 

 According to the nature of the pericarp fruits are divided into: 



{(I) dry fruits, in which the pericarp is membranous, leathery, 

 or woody; they either open naturally (dehiscent fruits) to let 

 the seeds out, or they remain unopened (indehiscent fruits) 



{!)) fleshy fruits, in wliicli the pericarp is either partially 

 (drupes) or wholly (berries) pulpy. 



Dry dehiscent fruits. 



The simplest form of this kind is a capsule originating from 

 a single carpel and bearing the seeds at its ventral suture. If 



