52 



PLANT GROWTH AND NUTRITION 



'Remains of sf-i^a 

 and sf/le 



Funiculus 



Microp/le 

 Hilum 



What makes a Seed grow. — The general purpose of the pages 

 that follow will be to explain how the baby plant, or embryo, 



is able to grow into an adult plant. 

 Two sets of factoi's are necessary for 

 its growth : first, the presence of 

 food to give the young plant a start ; 

 second, certain stimulating factors 

 outside the young plant, such as air, 

 moisture, and warmth. 



If we open a bean pod, we find the 

 seeds lying along one edge of the 

 pod, each one attached to the inner 

 wall by a little stalk. If we pull a 

 single bean seed from its attach- 

 ment, we see that the stalk leaves a 

 scar on the coat of the bean: this 

 scar is called the hi'lum. The thick 

 outer coat {testa) is readily removed 

 from a soaked bean, the delicate coat 

 under it easily escaping notice. The 

 seed separates into two parts ; these 

 are called the cotyle'dons. If jqm 

 pull apart the cotyledons very care- 

 fully, you find certain other structures between them. The rod- 

 like part is called the hypocofyl (meaning under the cotyledons). 

 This will later form the 

 root (and part of the stem) <:c^///^c/o/7^...=«..===— =...,,^re./a 



of the young bean plant. 

 The first true leaves, very ^'"^'■/^^ 

 tiny structures, are folded 

 together between the coty- 

 ledons, and are known as 

 the plu'mule or epicot'yl 

 (meaning above the cotyle- 

 dons) . All the parts of the 

 seed within the seed coats together form the embryo or young 

 plant. A bean seed contains, then, a tiny plant protected by 

 a tough coat. 



-Calyx 

 'Receptacle 



Bean pod and enlarged bean. 

 The pistil of the flower of the bean 

 plant becomes the fruit. The ovules 

 develop into the seeds, and the egg 

 cell becomes the embryo. 



Hilum 



A section through the bean shows that the 

 embryo is made up of undeveloped leaves, the 

 plumule ; an undeveloped shoot, the hypocotyl ; 

 and nourishing structures, the cotyledons. 



