178 BOTANY OF CROP PLANTS 



maximum ii4.8°F., and minimum 4i°F. Sturtevant further 

 shows that corn germinates in from ten to twenty days at 

 a temperature of 43.7°F., while at from 48.6°F., to 58.5°F., 

 it germinates in from five to ten days. In germination, the 

 primary root appears first, at the tip of grain; soon the plu- 

 mule breaks through the pericarp at about the middle of the 

 grain. The young germinating grain consists of a primary 

 root projecting at the peduncle end, and the plumule emerg- 

 ing through a slit in the pericarp at about the middle of the 

 grain, and pointing in the opposite direction. On the sides 

 of the primary root, two secondary ones soon appear, making 

 a total of three roots in the primary root system. 



In the seedling, there is, as in other cereals, a more or 

 less elongated axis between the base of the coleoptile and 

 the grain. This has been named the mesocotyl by some mor- 

 phologists. Collins described seedlings of maize grown by 

 the Indian tribes of the southwestern United States, that 

 may develop, under conditions of deep planting, a mesocotyl 

 up to 36 centimeters in length. 



Classification. — The many different varieties of cultivated 

 corn are all included under the one name, Zea mays L. 

 Sturtevant has divided this species up into "species groups" 

 (subspecies), the most important of which are the following:* 



1. Zea tunicata, pod corn. 



2. Zea everta, pop corn. 



3. Zea indurata, flint corn. 



4. Zea indentata, dent corn. 



5. Zea amylacea, soft corn. 



6. Zea saccharata, sweet corn. 



7. Zea amylea-saccharata, starchy sweet corn. 



*The specific name "mays" is omitted, for convenience, from the 

 following. 



