392 



SCIENCE 



[N. S. Vol. XL VI. No. 1190 



Perhaps in no one instance of reported re- 

 sistance to disease and insect attack has the 

 nature of the immunity been fully ascer- 

 tained or circumscribed, although it is gener- 

 ally conceded as being highly desirable to 

 determine the particular immimizing proper- 

 ties. In some cases it is thought to be due to 

 hardiness of the individual, or vigor of grovrth ; 

 in others, to the durability, composition, or 

 peculiarity of structure of the affected tissue. 



In the plantlet stage of growth there is not 

 much diiference between the corn and the 

 teosinte except that the leaves and stem of the 

 latter are narrower and more slender. As the 

 plants grovsr older the leaves of the teosinte are 

 tougher and more leathery in texture, with pro- 

 nounced teeth along the edges of the leaf. 

 The corn leaves become slashed and torn to 

 ribbons by wind storms, while the long narrow, 

 and tough leaves of the teosinte remain entire. 

 The sap of the corn plant is sweeter than the 

 sap of the teosinte. 



In the above-mentioned features the F^ re- 

 sembles the teosinte more than it does the 

 com. Since the aphis are sap suckers, the 

 sweeter juice and more readily penetrated epi- 

 dermis of the corn plant may be the deciding 

 factors of immunity for the teosinte and the 

 hybrid. This remarkable immunity appar- 

 ently provided material upon insect parasitism 

 as a means of determining genetic relation- 

 ship and elucidation of the problem of inher- 

 itance of immunizing properties in plants. 

 W. B. Gerneet 



Illinois Agricultural Experiment Station, 

 Urbana, III. 



SPECIAL ARTICLES 

 THE TILLERING OF WHEAT 



During the past eight years the writer has 

 made a rather extended study of the tillering 

 of winter wheat. The factors studied may 

 be divided into two general classes, viz., he- 

 redity and environment. It has been found 

 that the tendency to tiller appears to be 

 largely a varietal characteristic. In order to 

 study the behavior of the wheat plant with 

 respect to tillering it was found necessary to 



plant the kernels in hills 6 by 6 in. apart. 

 Two kernels were planted and later the plants 

 thinned to one per hill. This method of seed- 

 ing allowed the plant sufficient space to ex- 

 press rather fully its tendency to tiller. Seed- 

 ings were also made by drilling in rows as is 

 usually done in practical wheat culture. In 

 this case, however, the number of tillers per 

 plant could not be so accurately determined 

 at harvest owing to the crowded condition of 

 the plants in the row. As the plants came 

 up the number was determined for a definite 

 length of drill row. At harvest the total niim- 

 ber of culms within this space was noted and 

 divided by the number of plants. This gave 

 the average number of tillers per plant. 

 Where the wheat was seeded in hills each plant 

 was cut separately and the culms counted. 

 The mean for each variety was then deter- 

 mined by dividing the total number of culms 

 by the number of plants. More than 150 

 varieties and strains of winter wheat were 

 included in these tests. It was noted that the 

 bearded wheats as a class seem to tiller more 

 freely than the smooth. In order to test this 

 characteristic of varieties more thoroughly 

 identical varieties were grown the same season 

 on both fertilized and untreated soil. All of 

 the experiments were conducted in the field. 

 The following table gives the average number • 

 of tillers per plant for four varieties of wheat, 

 two smooth and two bearded. 



TABLE I 



Number of Tillers per Plant of Four Varieties 

 Grown under Different Conditions 



