? AND WORK OF PLANTS 



Fig. 2. 



Bean seeds soaking and swelling; read 

 from left to right. 



.consequently swell faster and become much 

 Syfinkied. The seed coats thus become loosened from the embryo 

 within and can be easily slipped off. After a time the embryo 

 swells by imbibition of water and the seed becomes plump again. 

 When the seed is split in two lengthwise by cutting the seed coats 

 along the convex side, the two halves can be laid open. These 

 two fleshy bodies are the seed leaves or cotyledons, and the rest of 



the embryo is attached at one 

 end to one of the halves, its attach- 

 ment being broken away from the 

 other. The root or radicle lies at 

 one end next the seed coats and in 

 the entire bean seed causes the 

 short elevated line at this end 

 of the seed. At the opposite end 

 is the plumule, consisting of two or four membranous leaves now 

 somewhat triangular in form and marked with fine lines or veins. 

 The stem of the embryo is short, and is that part of the embryo 

 to the upper end of which the cotyledons are attached, and to 

 the lower end of which the radicle is attached. This part of the 

 stem is the hypocotyl. 



3. Germination of the bean. In germination the radicle 

 elongates more rapidly at first than 

 the other parts, soon pierces the 

 seed coat near the scar and forms 

 a long, slender, conical, primary 

 root. The root hairs soon appear, 

 forming a dense velvety covering 

 over the root a little distance back 

 from the tip. As the stem, and 

 leaves of the plumule, which lie 

 between the cotyledons, increase in 

 size the seed coats are ruptured 

 by the pressure and are usually 

 cast off in the soil. The part of the stem which lies be- 

 tween the cotyledons and the root now elongates very rapidly 



Fig. 3- 



Bean seed split in two, showing plantlet 

 (radicle and plumule) at one end. 



