HEAT- 153 



juices, the loss of their excitability, and the chemical disturb- 

 ance ot'all their contents." 



•J'20. Prof. Liniliey's conclusions on this bubject, coincide 

 iu many respects with the conclusions of Prof. Morrcn, but in 

 «onje important points they dilFcr, Prof. Lindley remarks, that 

 in the most succulont si)ecies of plants, he did not find the vesi- 

 <*les of the celhdar tissue, separable from each other ; aiiu 

 that in several instances he t'ountl them lacerated, as if by the 

 distention of the fluid they had contained. He viso gives as one 

 of his conclusions: "A chemical deconiposition of the tissue 

 and its contents, especially the chlorophyll," which is at va- 

 riance with the seco' d conclusion of Prof. i\I. above. 



'J27. Tiie displacement of the lluids by freezing, is one of 

 the most curious tjnd interesting phenomena connected with 

 this subject ; and it would appear one of the most iujportant. 

 Prof. L. supposes, that the dilference in the etfect produced 

 by freezing, when frozen plants are thawed sudilenly, or by 

 c|egrees, is owing to the gradual return of the fluids to their 

 appropriate vessels, when gradually thawed, and that when 

 heat is suddenly applied, the air is expanded, and increases 

 the disturbance alrealy produced by its e\i)ulsion I'rom the 

 air cavities. We arc all well aware of the fact, that it makes 

 a great dilVerence in the eflccts of a frost on vegetables, wheth- 

 er thev are suddenly or jriaduallv thawed. The gardener of- 

 ten preserves plants, which would otherwise inevitably per- 

 ish, though perhaps not completely frozen in such cases, by 

 watering them someiimc before sun rise on a frosty morning, 

 with well or spring water ; by the application of a tem])era- 

 ture, but a ihw degrees above freezing, the plant thaws grad- 

 ually, and permits the air 'Mo retract by degrees tVojn its 

 new situation, without pVoducing additional derangement of 

 the tissue." But if permitted to remain till the rays of the 

 i^un come upon them, destruction is inevitable. Apples and 

 Potatoes also, if immersed in well waler while frozen, are in- 

 jured less by the frost, than they would be if permitted to be 

 thawed by a more elevated temperature. 



229. The eflect of frost in converting starch into sugar, is 

 well exhibited in the potatoe. This tuber when frozen, is de- 

 cidedly sweet, and the stareh which it before possessed in 

 great quantities, has in a great measure disappeared. 



229. "Finally" says Prof. L. *• it appears that frost exer- 

 cises a sppcific action upon the latex, destroying the power of 

 motion. If as Prof. Shullz supi)oses, this is the vital fluid of 

 plants, such a fact alone would account for the fatal efllcts 



