from the Stems of Vegetables. 335 



foliation continues from nightto night when the weather is suffi- 

 ciently cold, while all the earthy matter which is thus thrown 

 down is carried off by the first considerable fall of rain, it is 

 sufficiently obvious that it is a powerful agent of disintegration. 

 When the weather is not severe, it is only exhibited in situa- 

 tions most favourable to the production of cold. The pre- 

 sence of a twig or a straw on the surface of the clay will, under 

 these circumstances, determine the place of development of 

 the phaenomenon ; and a twig will thereby be elevated above 

 the general surface, supported by an elegant pectinated ar- 

 rangement of icy columns. 



4. On examination the icy columns were found to terminate 

 sharply at the surface of the clay, adhering so lightly as to be 

 detached by a mere touch of the finger, and scarcely ever con- 

 nected with any formation of ice below, — in fact, never, under 

 the circumstances most favourable to the development of the 

 phaenomenon. On the contrary, in the majority of cases, the 

 soil from which they protruded 'was not frozen in the slightest 

 degree, even during our severest weather, and when the earth 

 in other situations was completely incrusted. This point was 

 carefully examined early in the morning on the 11th of Janu- 

 ary 1849, when the thermometer was at 14° of Fahrenheit at 

 sunrise; again on the 17th of February, when it was at 12°; 

 and again on the 19th of the same month, when it stood as 

 low as 5°, — a most extraordinary degree of cold for this lati- 

 tude (34° N. lat.). These observations were carefully re- 

 peated on the mornings of the 4th, 5th, Gth, and 7th of Fe- 

 bruary 1850, when the temperature was respectively 16°, 14°, 

 18°, and 23° of Fahrenheit's scale at sunrise. On none of 

 these occasions was the ground, where the icy columns were 

 developed in profusion, frozen in the slightest degree. The 

 afternoon of February 4, 1850, affiarded me the rare oppor- 

 tunity of observing the phaenomenon in the very act of deve- 

 lopment. It took place on an eastern exposure at 5| p.m., 

 when the temperature was 28° F. As the day was very cold, 

 the icy columns of the previous night, which were about three 

 inches in length, had been only partially melted, in this pro- 

 tected situation, by the influence of the mid-day sun. At the 

 time the observation was made, these columns were found to 

 be elevated about one inch by the recently protruded ice. 

 The line of demarcation between the old and neiso ice-forma- 

 tion was perfectly distinct, the lower portions of the former 

 having been remarkably attenuated by the process of lique- 

 faction during the heat of the day. In this case it was obvious 

 that the evolution of the phaenomenon during the previous 

 night and morning had been temporarily checked by the solar 



