from the Stems of Vegetables, 341 



glass, are protruded, fed by the humidity conveyed through 

 its substance, and forming in their aggregation a fine silvery 

 surface, analogous to that of fibrous gypsum or satin spar." 

 (Supplement to Encyclopedia Britantiica, vol. iii. art. Coldf 

 p. 258.) The same elevating cause must have been in opera- 

 tion during the progress of this experiment, which produces 

 the protrusion of icy columns from the earth*. 



The phaenomenon manifested on certain plants is every way 

 analogous to that relating to the protrusion of ice from certain 

 kinds of soil, and admits of the same explanation. The porous 

 pith furnishes a constant supply of warm water from the earth, 

 while the wedge-shaped medullary rays secure the mechanical 

 conditions necessary for the development of a projectile force 

 in the proper direction. In proof of this it may be remarked, 

 that the medullary rays are very conspicuous in the Pluchea ; 

 and when the stalk is split by the freezing of the water within, 

 the fissure is observed to follow their course. The development 

 of the phaenomenon is arrested when the pith becomes frozen, 

 for the obvious reason that the consequent splitting of the stem 

 destroys the arrangement of resisting tubes. For a like reason 

 it is exhibited lo^yer down the stalk when it becomes rifted ; 

 for the conditions essential to its production are there found. 

 When the cold-producing cause is not too intense, the stalk 

 is not frozen, for the same reason that the ground remains 

 unfrozen under similar circumstances. The reason why the 

 phaenomenon is manifested only in certain kinds of plants, 

 probably arises from several peculiarities in their physical con- 

 dition. They must be porous to furnish an abundant supply 

 of fluid; they must be herbaceous and annual to secure me- 

 dullary rays of sufficient size and openness ; and it is probable 

 that all vital action must have ceased, in order that the fluid 



* Since writing the above, my attention has been called to analogous 

 phaenomena developed during the crystallization of certain salts. 



If the smaller portions of the soft and spongy roots of our common cy- 

 press {Ciipressus disticha, Mich.) be thoroughly soaked in a solution of 

 nitrate of potash, and exposed to the drying influence of the air at ordinary 

 temperatures, the whole surface will in process of time be covered with a 

 most delicate investment of hair-like crystalline fibres. They are always 

 observed to emanate at right angles to the convex surface of the root in 

 the form of radial prolongations, and often extend out from the wood to a 

 distance equal to, or exceeding its semi-diameter. When brushed off by 

 the finger, a fresh crop speedily appears. A similar exudation of crystal- 

 line filaments of sulphate of zinc is frequently observed on the surface of 

 the porous earthenware cups used in Grove's battery, when they are not 

 carefully washed. It is obvious that these phaenomena are identical in 

 their origin with the protrusion of the columns of ice from the earth, ex- 

 cepting that in the latter case the influence of cold is essential to the pro- 

 cess of crystallization. 



