CHAPTER II. 



PARTS OF SEEDS AND HOW SEEDS GERMINATE. 

 THE BEAN. 



8. Seed of the common garden bean. There are many 

 varieties of garden beans but the form of the seed is often slightly 

 curved or kidney-shaped as seen in side view. Upon the concave 

 side there are distinct markings. There is a scar ( = hilum) about 

 the middle line. This is the point where the seed was attached 

 to the wall of the bean pod as can easily be seen in the case of 

 young beans by opening the pods. Near either end of the scar 

 is a minute mark. One of these is slightly larger than the other 

 and often appears when examined under a hand lens to be some- 

 what heart-shaped. It is continuous with a 

 short raised line on that end of the bean.* 

 Near the other end of the scar is a minute 

 opening, the micropyle. The root of the embryo 



t... ..-.-* (the young plant in the seed) lies beyond this 

 :'.'! just underneath the seed coats. Its position is 



often manifest by a prominent elongated eleva- 

 tion, especially when the bean is swollen after 

 soaking in water. 



9. Parts of the bean seed. When beans 

 are soaked for a few hours in water the seed 

 coats take up the water faster than the embryo 

 and consequently swell faster and become much wrinkled. 

 The seed coats thus become loosened from the embryo within 

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



*This slightly elevated line is the raphe (fig. 4). It is formed by the stalk 

 of the ovule (the very young stage of the seed in the pod) which is attached 

 at the end of the bean and here is bent around and joined to the edge. 



6 



7rt 



h 



r-r 

 c 



Fig. 4. 



Bean seed; rad. rad- 

 icle as primary root 

 (under the seed coat) ; 

 m. micropyle; h. 

 hilum; r. raphe; c. 

 chalaza. 



