14 



PRACTICAL COURSE IN BOTANY 



17 18 



Figs. 17, 18. — A kid- 

 ney bean : 17, side view : 

 18, front \new, showing /j, 

 liilum, m, micropyle. 



12. Dissection of a bean. — Sketch a dry bean as it lies in 

 the pod, showing its point of attachment and any markings 

 that may appear on its surface. Then take it from the pod and 

 examine the narrow edge by which it was attached. Notice 

 the rather large scar (commonly called the eye of the bean) 

 where it broke away from the point of 

 attachment. This is the hilum. Near the 

 hilum, look for a minute round pore hke 

 a pinhole. This is called the micropyle, 

 from a Greek word meaning " a little 

 gate," because it is the entrance to the 

 interior of the seed coat. There was no 

 micropyle observed in the corn grain, 

 because it is not a true seed but a fruit 

 inclosing a single seed. The inclosing 

 membrane is the fruit skin, w^hich has become incorporated 

 wdth the seed coat and taken its place as a protective covering. 

 Compare a soaked bean with a dry one ; what difference do 

 you perceive ? How do you account for the change in size and 

 hardness? Find the hilum and the micropyle in the soaked 

 bean. Lay it on one side and sketch, with the micropyle on 

 top ; then turn toward you the narrow edge that 

 was attached to the pod and sketch, labeling all 

 the parts. ]\Iake a section through the long diam- 

 eter at right angles to the flat sides, press it 

 slightly open, and sketch it. Notice the line or 

 slit that seems to cut the section in half longitu- 

 dinally, and the small round object between the 

 halves at one end ; can you tell what it is ? 



Slip off the coat from a whole bean and notice its 

 texture. Hold it up to the light and see if it shows 

 any signs of veining. See whether the scar at the hilum extends 

 through the kernel, or marks only the seed coat. Lay open the 

 two flat bodies into which the kernel divides when stripped of 

 its coats, keeping them side by side, with the part above the 

 micropyle toward the top. Sketch their inner face and label 



