72 



BOTANY 



Push back the husk of a young ear of corn. The husk is simply 

 a covering of leaflike parts which has grown over the young 

 fruits for their better protection. We have already noticed such 



a structure forming the capsule of the acorn 

 and bur of chestnut. What did we call it ? 

 We uncover what was a short time before 

 a bunch of ver}^ peculiar flowers. The corn 

 cob is the much-thickened flower stalk on 

 which the flowers were clustered. If you 

 have removed the husk carefully you will 

 see part of each flower remaining attached 

 to each grain of corn. The so-called silk of 

 corn is nothing more than a long central 

 style and stigma. The corn grain itself was 

 also part of the flower — the same part 

 that formed the pod of the bean with its 

 contained seeds. The corn grain, therefore, 

 is a fruit and not a seed. Is the grain of 

 corn homologous with the pea or bean? 



Laboratory Suggestions for Work on Grain of 

 Corn? — In a single grain of corn which has been 

 soaked at least twenty-four hours, notice the differ- 

 ences between the attached and free ends of the 

 grain. Look for the scar which marked the at- 

 tachment of the silk. The light-colored area 

 found on one surface marks the position of the 

 embryo ; the rest of the grain contains the endo- 

 sperm. Cut a grain perpendicular to the flat side 

 of the grain in a lengthwise direction. Find the 

 embryo from its relation to the outside of the 

 grain. Apply a drop of weak iodine solution. 

 What material is found in the endosperm of corn ? 

 The part of the grain that does not stain so 

 deeply with iodine is the embryo. Find two parts, 

 — a tiny elongated structure and an area lying be- 

 tween it and the endosperm. The latter is the 

 single cotyledon. 



Use a lens. Notice that the elongated struc- 

 ture in the embryo has two parts, the hypocotyl 

 pointing toward the attached end and the plumule or the epicotyl point- 

 ing toward the unattached end. 



Draw the longitudinal section of the corn grain as seen stained with 

 iodine. Mark all the parts. Make your drawing at least twice natural size. 



Longitudinal section of 

 young ear of corn ; O, the 

 fruits; S, the stigmas; 

 SH, sheathiike leaves; 

 ST, the flower stalk or 

 peduncle. (After Sar- 

 gent.) 



' See Hunter and Valentine, Manual, page 16. 



