THE STEMS 



75 



The effect of the rainfall upon the number of straws produced by 

 the plant is strikingly exhibited in the results of some experiments 

 carried out during three years in order to determine the differences 

 between autumn- and spring-sown crops. 



Nineteen varieties were sown in October, and again in February, in 

 the seasons 1910-11, 1911-12, and 1912-13, the plants being grown in 

 rows six inches apart, the individual grain being deposited six inches 

 asunder in the rows. 



The average tillering power and the rainfall are given below : 



The heavy rainfall in the winter of 1911-12 reduced the straws per 

 plant to about half the number obtained in the previous and succeeding 

 drier seasons, the effect being seen not only in the autumn- but in the 

 spring-sown crops. 



It was found also that grains sown in spring very frequently produced 

 more straws and ears, though always of less average weight than those of 

 the same variety sown some three or four months earlier in the previous 

 autumn, the increase being most marked in the rapid-growing spring 

 wheats of normally short vegetative period. 



The table on the following page gives the number of straws and ears 

 per plant produced by five typical winter and four spring wheats, sown in 

 autumn (Oct.) and spring (Feb.) respectively, during three successive seasons. 



Tillering only continues so long as the temperature is above the 

 minimum for growth, and is most rapid at the optimum temperature : 

 it almost ceases in mid- winter, but goes on to an almost equal extent in 

 autumn and spring. 



The date of sowing also influences tillering, since the degree of warmth 

 and the amount of light available for the plant as well as the length of time 

 for assimilation and vegetative growth are all correlated with it. Wheat 

 sown early in autumn branches more than it does when sown later, 

 although in most seasons the difference in the number of straws per plant 

 is comparatively small among crops drilled at any time between late 

 October and the end of January. It is in plants produced from grains 



