512 Transactions of the London Horticultural Society. 



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 con- 

 siderable part of it disappears, and the remainder loses its transparency, 

 becomes fusiform, is sometimes surrounded by coagulated gelatinous colourless 

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

 taneous parenchyma of the leaf of Hibiscus Rosa Sinensis, the vesicles forming 

 the sides of the air chambers are filled "with distinct, angular, deep green par- 

 ticles, which, after freezing, become amorphous, and seem as if partially dis- 

 solved. It is possibly to the decomposition, 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 amylaceous matter, which is so abundant in many plants, also under- 

 goes 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 par- 

 ticularly striking in Hibiscus militaris. 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 pai't of the starch disappears, and the particles which remain are 

 not more than a half or quarter their former size. I have not, however, re- 

 marked among them any appearance of dissolving; neither have I been able to 

 observe any change in the curious double-headed bodies, in form resembling 

 dumb-bells, found in the vessels of Euphorbias, and supposed to be a state of 

 amylaceous matter, because iodine colours them violet ; they appeared to me 

 to be in precisely the same state before and after the plant was frozen to death. 

 M. Payen, however, denies that any starch whatever is lost in frozen potatoes 

 (^Compfes rendus, vi. S'tS.); but as only a small part of his important treatise 

 on amylaceous matter has reached this country, I am unable to state in what 

 way he explains the action of cold upon this substance. 



" Finally, it appears that frost exercises a specific action upon the latex, de- 

 stroying its power of motion. If, as Professor Schultz supposes, this is the 

 vital fluid of plants, such a fact would alone account for the fatal effects of 

 a low temperature. In all the cases I have observed frost coagulates this 

 fluid, collecting it into amorphous masses. In Stapelia, where the laticiferous 

 vessels are easily found, the latex itself is so transparent, that it is difficult to 

 perceive it in a living state, even with the best glasses ; but after freezing it 

 is distinctly visible, resembling half coagulated water. In the Hibiscus above 

 mentioned, the stem is covered with long, rigid, simple hairs, filled with a 

 plexus of capillary laticiferous vessels of extreme tenuity, but in which the 

 motion of the latex may be seen beautifully with the -i- of an inch object 

 glass of an achromatic microscope. Upon being thawed, after freezing, all 

 this apparatus is found reduced to some misshapen separate sacs of fine gru- 

 mous matter, in which no motion can be detected. That these vessels lose 

 their vitality after freezing, may indeed be seen without the aid of a micro- 

 scope ; for if a stem of a Ficus elastica, or a Euphorbia, or any such plant, 

 which discharges an abundance of milk when wounded, be first frozen, and 

 then thawed, no milk will follow the incision. 



" From these facts, I think we must draw the conclusion, that the fatal effect 

 of frost upon plants is a more complicated action than has been supposed ; of 

 which the following are the more important phgenomena : — _ 



