330 Dr. LeConte on a remarkable Exudation of Ice 



held in check by the extreme paucity of facts and observations, 

 so that no explanation of them has been advanced. 



For many years my attention has been drawn to the re- 

 markable deposition of ice around the stalks of certain plants, 

 as well as to analogous phaenomena exhibited by certain kinds 

 of soil. During a visit to the sea-coast of Georgia in the 

 months of November and December 1848, I had a very fa- 

 vourable opportunity of studying the phaenomenon as exhi- 

 bited in vegetables. The plants in which I have observed it 

 are two species of the genus Pluchea of DeCandolle, or Conyza 

 of the older botanists, viz. Pluchea hifrons and P. camphorata. 

 It is more common and conspicuous in the former species than 

 the latter. Both of these plants grow abundantly in wet soils, 

 around ponds and along the road-side ditches in the low 

 country of Carolina and Georgia. The root is perennial, but 

 the stem is annual and herbaceous. 



The exudations of ice are most abundant and striking 

 during the first clear frosty weather in November and De- 

 cember. At this period the earth is warm ; and the serenity 

 of the atmosphere is so favourable to radiation, that there is a 

 remarkable difference between the temperature of the day and 

 night. When the temperature sinks towards daylight to about 

 30° or 28° of Fahrenheit, or even lower, the surface of the 

 ground is totally devoid of the slightest incrusting film of 

 frozen earth, while hoar-frost is deposited in such profusion 

 on all dead vegetable matter as to resemble a slight fall of 

 snow. Under such circumstances, the traveller who passes 

 along the level roads of this region soon after sunrise cannot 

 fail to be struck with the remarkable accumulations of volu- 

 minous friable masses of semi-pellucid ice around the foot- 

 stalks of the Pluchea which grow along the road-side ditches. 

 At a distance they present an appearance resembling locks of 

 cotton-wool, varying from four to five inches in diameter, 

 placed around the roots of the plants; and when numerous, 

 the effect is striking and beautiful. 



In relation to the exudation of ice from the stems of vege- 

 tables, the description and delineation given by Sir John Her- 

 schel are so clear and faithful, and accord so exactly with the 

 results of my own observations, that I prefer using the lan- 

 guage of that justly distinguished philosopher whenever it suits 

 my purpose. The engraving which accompanies his paper 

 represents the appearances presented very accurately*. My 

 observations appear to establish the following facts in relation 

 to this phaenomenon : — 



* The reader is requested to refer to the engraving given by Sir John 

 Herscbel in the Philosophical Magazine for February 1833, 



