171 



ftnd terminated by only a short point, has only rarely large plump 

 beans ; they are bitter and of a bright violet colour. The worst is a 

 variety of which the fruits are deep red, bright, smooth, with thick 

 shell, rounded at the two ends and massive, of which the beans are 

 very flat, of a deep violet colour and very bitter. It is called " Tri- 

 nitario Amergo" or " Cojon de Toro," fermentation for this variety 

 ought to last 8 days, and even then its taste is still bitter and acrid. 



SOIL TEMPERATURE. 



Reference was made in last bulletin (page 126) to the temperature 

 of the soil. Prof. F. H King in his " Text Book of the Physics 

 of Agriculture," which everyone interested in agriculture should pos- 

 sess, has a chapter on the subject, from which the following notes are 

 taken. 



Importance. In temperate climates subject to frost, growth will not 

 begin, with most cultivated crops, until the soil has attained a temper- 

 ature of 45° to 48° F. and it does not take place most vigorously until 

 after it has reached 68° to 70° F. Neither do the nitre germs begin, 

 the formation of nitric acid from humus until a temperature above 

 41° F. has been reached and its greatest activity is not attained until 

 the soil temperature has risen to 98° F. 



Germination. The soil temperatures at which the seeds of most 

 cultivated crops germinate best, lie between 70° and 100° F. with an 

 average of about 85° F. The best soil temperature for germination 

 of corn (maize) and squash is 93°, for melon 99 '^. The more quickly 

 seeds are permitted to germinate after they are placed in the soil 

 the higher will be the per cent, of seeds growing, and, as a 

 rule, the more vigorous will the plants be. Indeed seeds of low 

 vitality placed in too cold a soil often fail to germinate at all. It is 

 found that, when corn germinates in 3 days at a temperature of 65 3° 

 F,, it requires 11 days when the soil was as low as 51° F. 



Root Pressure. The power which sends the soil moisture into the 

 roots of plants and up into the leaves is osmotic pressure, developed by 

 the warmth of the soil, and unless the soil temperature is sufficiently 

 high, plants may wilt. Pumpkin and tobacco plants wilt badly, 

 even at night with an abundance of moisture, as soon as the soil tem- 

 perature falls much below 55° F., the moisture not rising fast enough 

 to compensate for even the slow evaporation during the night. 



Formation of Nitrates. The nitrates in the soil do not develop until 

 the temperature has risen above 41° F. ; the action of the germs is ex- 

 tremely feeble at 54° and they do not attain their maximum activity 

 until a soil temperature of 98° has been reached ; but if the earth be- 

 comes as warm as 113° F. then the action is nearly stopped, it being 

 as weak as at 54°. 



Inflmnce of colour. The colour of a soil, especially when dry, so 

 that the rate of evaporation from its surface is small, has a marked in- 

 ;fluence on the temperature, eveu at considerable depths. The darkest 



