Apr. 8, i9i8 Effect of Meteorological Factors on Sorghums 145 



variable, but Blackhull kafir 17569, Sumac sorgo 17554, a-^d most of the 

 other varieties Hsted are standard strains which are known to be stable. 

 Blackhull kafir showed a difference of 3 in the number of leaves under 

 the differing conditions, and Sumac sorgo had 6 more leaves at Bard 

 than at Chula Vista. Evidently unfavorable conditions of growth 

 cause a reduction in the number of leaves and this character is, therefore, 

 of uncertain value as a basis of classification or botanical description. 

 Table IV is even more interesting for the study of individual varieties 

 than it is in a study of the average variation. Thus, Dwarf hegari. 

 Dwarf and Standard milos, and Sumac, Collier, Florida, and Orange 

 sorgos show a striking difference in height under different weather 

 conditions, while the other varieties vary much less in height, but fully 

 as much or more than above-named sorts in the size of the leaf and 

 panicle. 



EFFECT OF THE DATE OF PLANTING ON THE GROWTH OF SORGHUMS 



The effect of different dates of planting on the growth of sorghum 

 plants is set forth in Table V. Other things being equal, this effect 

 apparently is correlated with the presence of high temperatures at 

 different periods of the life cycle. In 191 5, when the plantings were 

 made in April, the early stages of growth took place in a period of moderate 

 temperatures, and the flowering and fruiting functions were carried 

 on in a period of very high temperatures. In 191 6 the plantings were 

 made about the middle of June. Growth began during a period of high 

 temperatures and maturity took place when conditions were more 

 moderate. 



A study of Table I in connection with Table V shows the relation 

 that the period of high summer temperatures bears to the growing 

 periods of each planting. The conditions in 191 6 were practically the 

 same as in 1915. A comparison of the mean temperatures with the nor- 

 mals shows how uniform the seasons are at Bard. 



An examination of Table V shows that deferring the planting date 

 55.5 days shortened the growing season for the 12 varieties under test 

 an average of 21 days. In spite of the shorter growing season in 191 6 

 the total of positive heat units available during the period of growth in 

 the two years was practically the same, 4,628° F. in 1915 and 4,318° in 

 1 91 6. The early date of planting and longer growing season produced 

 taller plants and longer leaves, but in all other characters the excess in 

 magnitude was with the later planting. On the whole, the plants from 

 the later planting were more nearly normal in their growth and produced 

 a better seed crop. It would appear, therefore, that more favorable con- 

 ditions of growth are obtained if the date of planting is regulated so that 

 the early stages of the plant's development coincide with a period of high 

 temperatures and the later stages, when the plant is nearing maturity, 

 come when moderate temperatures prevail. 



