306 Observations upon the effects of Frost, 



affected by so little as only two or three degrees of frost. In Stapelia, 

 when thawed, it is found collected into clusters, and apparently half 

 dissolved. In Euphorbia Tirucalli, when the plant is alive, it is 

 extremely abundant, and consists of distinct spheroidal transparent 

 particles, but, after a slight freezing, a considerable part of it dis- 

 appears, and the remainder loses its transparency, becomes fusiform, 

 is sometimes surrounded by coagulated gelatinous colourless matter, 

 and many of the particles appear as if burst. In the green subcu- 

 taneous parenchyma of the leaf of Hibiscus Rosa sinensis, the ve- 

 sicles forming the sides of the air chambers are filled with distinct, 

 angular, deep green particles, which, after freezing, become amor- 

 phous, and seem as if partially dissolved. It is possibly to the de- 

 composition, of which these appearances are the incipient signs, 

 that the extremely offensive odour of some frost-bitten plants, 

 especially the Laurustinus, when thawed, is to be ascribed. 



The amylacous matter, which is so abundant in many plants, also 

 undergoes alteration. This has been remarked by Professor 

 Morren, who found that when Potatoes are frozen, a part of their 

 starch disappears, leaving the deformed integuments behind it, and 

 he suspected that the starch thus lost had furnished the sugar formed 

 in the process of freezing this tuber. I believe it will be found a 

 general fact, that starch is materially altered by frost, for I have 

 always found that the amylaceous particles seem less abundant in a 

 plant after freezing than before, and of those which remain, a part 

 is generally becoming amorphous, clustered together, and certainly 

 diminished in size. This is particularly striking in Hibiscus mili- 

 taris. In that plant the cells of the pith abound in amylaceous 

 granules, and are often quite filled with them ; and they also occur 

 abundantly inside the cells of the bark, of the medullary rays, and 

 even of the tubes of the wood, and in short everywhere except 

 inside the woody tubes of the liber ; so that a thin slice of the stem of 

 this plant, treated with iodine, forms a most beautiful microscopical 

 object. But after being frozen, a great part of the starch disappears, 



