848 
Journal of Agricultural Research voi. xxiii, no h 
experiments by adding water at the same temperature as the soil. Data 
were taken on the number of plants emerging, rate of emergence, general 
appearance, rate of tillering, number of tillers; and in some few instances 
the plants were grown to maturity and the influence of soil temperature on 
maturation studied. Upon completion of the experiments the roots were 
carefully washed free from the soil, after which the length of roots, length 
of the subcrown intemode, height of the plants, and dry weight of roots 
and tops were determined separately. The data discussed in this chapter 
are given in condensed form in the seedling-blight discussion. The data 
indicate that the influence of soil temperature on the cereals tested seems 
to be greater during the germination period than at any other stage of 
their development. This is not, however, a new observation, as Gutzeit 
(12) and others have shown this to be true for other plants than the 
cereals. Sachs (« 24 ), Haberlandt {13; 14, p. 39-47 , 69-78 ), Bialoblocki 
(5), Vinall and Reed (31), and others have determined the cardinal tem¬ 
peratures for the germination of wheat, com, and other cereals. Still 
others, notably Kincer (. 22 ), have attempted to correlate the critical 
temperatures for germination and date of seeding. 
The spring wheat emerged first at about 28° C., at which temperature 
it reached the surface in 38 to 48 hours. The rate of emergence decreased 
rapidly above this soil temperature—28°—and rather gradually below 
that temperature. The seedlings produced at soil temperatures above 
28° emerged very irregularly and developed unevenly. On the other 
hand, growth was very uniform at the lower soil temperatures, even at 8°. 
At this temperature it required ro to 12 days for the plants to emerge. 
The comparative rate of development of roots and plumules of the 
wheat seedlings at low and high soil temperatures was indicative of a 
distinctly different type of metabolism at the two temperature extremes. 
At the low temperatures, notably 8° and 12 0 C., the roots developed first 
and usually were several centimeters long before the plumule began to 
develop; whereas at the high temperatures, notably 28° to 32°, the 
plumule was well out of the soil before the roots developed. The low 
temperatures continued to stimulate root development until well towards 
the heading period, the largest root system for spring wheat developing 
at about 12 0 to 16 0 . 
Elongation of the subcrown intemode, the first intemodal region 
between the seed and the first node, was greatly stimulated by high soil 
temperatures. At 24 0 C. and above, the secondary roots developed at or 
near the soil surface, while at 8° subcrown intemode elongation was 
almost entirely inhibited, the first node and secondary roots developing 
immediately above the seed. This inhibition of the subcrown intemode 
at low temperatures persisted even when the seeds were sown at consid¬ 
erable depths below the surface. At temperatures of 16 0 or above, how¬ 
ever, deep seeding or a moist dark compartment greatly increased the 
length of this region, bringing the secondary roots near the surface of 
the soil. The response of these tissues to environing factors has been 
described by Schroeder (26 ), Vogt (52), Halsted and Waksman (15), and 
others. 
Elongation of the coleoptile, on the other hand, was inhibited by high 
soil temperatures. At temperatures above 20° C., the growing point of 
the culm always broke through the coleoptile before emerging from the 
soil. At temperatures below 16 0 , however, the coleoptile elongated very 
much faster than the growing point of the culm and as a result inclosed 
the growing culm until after emergence, thus preventing the young 
