HORTICULTURAL JOURNAL. 359 



nomenon was strictly confined to exotic species cultivated in the open 

 ground, and consequently with their roots well developed and capable of 

 imbibing large quantities of fluid without intermission. It occurred, more- 

 over, on the first night that the temperature of the air and surface of the 

 ground descended, except as a transient minimum, in a marked degree 

 below the freezing point, and that accompanied by a strong dry wind, which 

 must have been very favorable to evaporation. The accompanying illustra- 

 tion represents a small portion of a branch with either kind of formation, 

 the prickly twig of Lantana aculeata exhibiting the first species, while the 

 second is a Cuphea cordata. 



This curious formation admits of more than one explanation. Le Conte 

 regards it as a purely physical phenomenon, while De Caspary, neglecting 

 Herschel's view, leaves it uncertain whether the ice arises from the plant 

 itself, or from the comparatively warm earth beneath, the evaporation from 

 which is conveyed upwards by the plant, as by a kind of chimney. Le 

 Conte considers the lamellar formation on the plants of the same nature 

 with the pillars of ice, consisting of innumerable thread-like spun glass, 

 which sometimes snring from the surface of the soil, arising from the innu- 

 merable capillary tubes which are contained in its substance. These masses 

 occur only on the surface of the soil, which itself remains unfrozen. Sup- 

 posing, then, a loose and warm soil to be saturated with moisture and 

 exposed to moderate frost, since the soil is a bad conductor of heat, the 

 uppermost stratum alone would be cooled down to the freezing point: and 

 since the resistance to lateral expansion is less on the surface than it is 

 lower down, the first effect of cold will be to make the ends of the capillary 

 tubes or pores conical or pyramidal. The sudden chilling of the surface- 

 ivater produces a rapid and forcible expansion, which, in consequence of the 

 resistance offered by the sides of the cones, not merely pushes the thready 

 pillar of ice forwards, but also causes it to protrude in the direction of least 

 resistance, namely, perpendicular to the surface. The conical extremities 

 thus become free,fresh fluid follows by capillary attraction from behind, the 

 formation and protrusion of ice is again effected, and the same process is 

 ?ated by paroxysms till a mass is formed three inches or more in length. 

 *-'• Xow if this be compared," says Le Conte, "with what takes place in the 

 Pluchea, similar conditions will be found to exist. The porous pith supplies 

 a constant flow of warm fluid from the soil, while the cuneiform medullary 

 : present the mechanical conditions necessary for the exercise of a pro- 

 trusive power in the required direction." 



It is not true that the moisture does ascend by the pith ; but making the 

 necessary corrections, it is easy to understand that masses of ice might be 



