30 



however, still depresses g-rovvth, probably because the lig'ht and 

 root temperature reductions are too great. 



Provided insolation is not excessive, the amount of daily 

 fluctuation of root temperature over a total range of about 22^ C. 

 (6.70 — 28.9° C.) has comparatively little influence upon growth; 

 high maxima and low minima give similar results to low maxima 

 and relatively high minima, pro\ ided the average mean tempera- 

 tures are not too dissimilar. With high root temperature a 

 difference in the degree of insolation or in the angle of incidence of 

 the sun's rays may have a considerable influence on growth, a 

 slight easing off of the solar conditions enabling much better 

 growth to be made. With very strong sunshine, reduction of high 

 maximum root temperatures (29° C. or above) allows of satisfactory 

 growth when unprotected plants are rapidly killed. The inhibi- 

 tory action of too high temperatures at the roots is thus clearly 

 shown. 



Nevertheless, the growth so made is less good than under more 

 normal conditions of insolation, thus demonstrating the harmful 

 action of too powerful sunlight, when all the root temperatures 

 rule high. 



Root temperatures appear to be of greater importance than 

 atmospheric temperatures, as good growth can be made in hot 

 atmospheres, provided the roots are kept relatively cool. There 

 is some reason to believe that the minima are of as much importance 

 as the maxima, i.e., that plants can withstand very high maximum 

 temperatures provided there is a considerable drop to the minima, 

 but cannot put up with the constant conditions of heat induced by 

 fairly high maxima and high minima. 



III. Kharak Singh. ''Development of Root System of 

 Wheat in Different Kinds of Soils and with Different 

 Methods of Watering.'' Annals of Botanv, 1922. 

 Vol. XXXVI. pp. 353-360. 



A study of the development of the root system in different kinds 

 of soil and under varying conditions of manuring, watering, and 

 cultivation, is of considerable importance in the Punjab (India), 

 especially where the crops have to depend mainly on artificial 

 irrigation. Duplicate pot experiments were carried out in which 

 wheat plants were grown in various kinds of soil, watering being 

 done on the surface in one case, and in the other through a small 

 porous pot sunk to the level of the soil in the middle of each large 

 pot, thus carrying the water directly to a lower level. The 

 observations were preliminary in nature, but indicate that wheat 

 plants in pots show better growth when watered from below than 

 when watered from above. The difference is greater in light soil 

 in the early stages of growth, but it is more marked in heavy soil 

 in the later stages of growth. 



Under the exjjerimental conditions the development of root and 

 shoot was best in pure sand, provided it was supplied with an 

 adequate amount of water and was underlaid by a layer of farm- 

 yard manure. The growth of wheat is better in a mixture 

 containing 25 per cent, sand and 75 per cent. Rothamsted soil, 

 than in pure Rothamsted soil, or in a mixture of 50 per cent, sand 

 and 50 per cent. Rothamsted soil. Moreover, wheat plants do not 



