142 



HEAT. 



of vegetable life. 6. That the expansion of the cells and aqui- 

 ferous organs drives a great quantity of water into the air-cells 

 and air-vessels, so that the apparatus intended to convey liquid 

 only, contains water and air, while that which is naturally a 

 vehicle for air conveys water. Such an inversion of functions 

 must necessarily be destructive to vegetable life, even if death 

 were not produced in frozen plants by the decomposition of their 

 juices, the loss of their excitability, and the chemical disturbance 

 of all their contents." 



271. Prof. Lindley's conclusions, on this subject, coincide in 

 many respects with the conclusions of Prof. Morren, but in some 

 important points they differ. Prof. Lindley remarks, that in the 

 most succulent species of plants, he did not find the vesicles of 

 the cellular tissue separable from each other ; and that in several 

 instances he found them lacerated, as if by the distension of the 

 fluid they had contained. He also gives as one of his con- 

 clusions, " A chemical decomposition of the tissue and its con- 

 tents, especially the chlorophyll,'' which is at variance with the 

 second conclusion of Prof. M, above. 



The displacement of the fluids by freezing is one of the most 

 curious and interesting phenomena connected with this subject ; 

 and it would appear one of the most important. Prof. L. sup- 

 poses that the difference in the effect produced by freezing, when 

 frozen plants are thawed suddenly, or by degrees, 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 already produced 

 by its expukion from the air-cavities. We are all well aware 

 of the fact, that it makes a great difference in the effects of a 

 frost on vegetables, whether they are suddenly or gradually 

 thawed. The gardener often preserves plants, which would 

 otherwise inevitably perish, though perhaps not completely 

 frozen in such cases, by watering them some time before sunrise 

 on a frosty morning with well or spring water ; by the applica- 

 tion of a temperature but a few degrees above freezing, the plant 

 thaws gradually, and permits the air '' to retract by degrees from 

 its new situation, without producing additional derangement of 

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

 come upon them, destruction is inevitable. Apples and Pota- 

 toes also, if immersed in well-water while frozen, are injured less 

 by the frost than they would be if permitted to be thawed by a 

 more elevated temperature. 



272. The effect of frost in converting starch into sugar is well 



271. What are Lindley's views?— 272. What effect on starch? 



