1 70 BOTANY OF CROP PLANTS 



viduals, protandry (anthers mature first) or protogyny 

 (stigmas mature first) may occur. Out of 2,794 individuals 

 in 59 varieties examined, he found 243 individuals homoga- 

 mous, 92 protogynous, and 2,459 protandrous. It appears, 

 then, that protandry is the rule in corn. In protandrous 

 individuals, the first appearance of silks occurred from one to 

 twenty-three days after pollen shedding, although the aver- 

 age is two days. Varieties of corn dealt with in the above 

 were pod, pop, flint, dent, soft, and sweet. Collins records 

 the discovery of the protogynous habit in a variety of maize 

 introduced from Granada, Spain. Ordinarily, however, 

 dichogamy is seldom pronounced enough to completely ex- 

 clude self-pollination. 



Gernert has also made observations as to the number of 

 days intervening between the appearance of tassel and 

 anthers. He finds, out of 3,319 individuals in 57 varieties, 

 that, in the greatest number (514), the anthers appeared 

 nine days after the tassel, and that in more than half of 

 the individuals the first anthers appeared in seven to ten 

 days after the tassels bearing them appeared. 



Pollen is produced in great quantities. It is estimated 

 that each tassel produces 20,000,000 to 50,000,000 grains of 

 pollen. Lazenby estimated that for each ovule in dent 

 maize there are about 45,000 pollen grains produced. 



The size of pollen grains in corn varies. Pollen produced 

 by central spikes is larger than that produced by laterals. 

 Livingston observed that in Leaming corn the pollen grains 

 from the central spikes were 0.02 milKmeter larger on the 

 average than those from lateral spikes. Of 12 varieties 

 examined, Gernert finds that the average diameter of the 

 pollen grain of corn varies from 0.08 to o.i millimeter. 

 They are rather ellipsoidal in shape. Corn pollen soon 

 shrivels after being shed, but its germinating power is not 



