DESTRUCTION OF PLANTS BY FROST. 



perature of' 27° are very different; they are softer, dull olive green, with a flaccid petiole, 

 and offer but little resistance to pressure: yet, although they give way freely, tlie quanti- 

 ty of air which the coinpressorium expels is comparatively small, and readily driven out. 

 Moreover, the long hairs of this plant, which in the natural state are occupied b}' fluid, 

 were alwa3S found filled with air after freezing, and this without pressure having been 

 exercised upon them. 



" I am inclined to refer to this cause the well-known fact, of which many cases occurred 

 this winter, that the sudden exposure of frozen plants to warmth will kill them; though 

 they msLy not suffer if warmed gradually. In such cases, it may be supposed that the 

 air, forced into parts not intended to contain it, is expanded violently, and thus increases the 

 disturbance already produced its by expulsion from the proper air cavities ; while, on the other 

 hand, when the thaw is gradual, the air maj' retreat by degrees from its new situation with- 

 out producing additional derangement of the tissue. It is also possible that leaves, from which 

 their natural air has been expelled by the act of freezing, may, from that circumstance, 

 have their tissue too little protected from the evaporating force of the solar rays, which 

 we know produce a specific stimulus of a powerful kind upon those organs. 



" These circumstances are, in themselves alone, sufficient to account for death being 

 produced in plants by frost; and it is chiefly to such as these, that Professor Morren has 

 directed his attention. It however appears to me that there are some other points of ini 

 portance to which observers have not applied themselves. 



" The green coloring matter of leaves, or chlorophyll, is certainly affected by so little 

 as only two or three degrees of frost. In Stapelia, when thawed, it is found collected in- 

 to 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 disappears, and the remainder loses 

 its transparencj', becomes fusiform, is sometimes surrounded by coagulated gelatinous color- 

 less matter, and many of the particles appear as if burst. In the green subcutaneous paren- 

 ch3'ma of the leaf of Hibiscus Rosa Sinensis, the vesiclesforming the sides of the air cham- 

 bers are filled with distinct, angular, deep green particles, which, after freezing, become 

 amorphous, and seem as if partially dissolved. It is possibly to the decomposition, of 

 which these appearances are the incipient signs, that the extremely offensive odor 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 undergoes altera- 

 tion. This has been remarked b}^ 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 al- 

 tered 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 be- 

 coming amorphous, clustered together, and certainly diminished in size. This is particu- 

 larly striking in Hibiscus militaris. In that plant the cells of the pith abound in amyla- 

 ceous granules, and are often quite filled with tliem; and they also occur abundantly in- 

 side the cells of the bark, of the medullary rays, and even of the tubes of the wood, and, 

 in short, everywhere except inside the wood)' tubes of the liber; so that a thin slice of 

 the stem of this plant, tieated with iodine, forms a most beautiful microscopical object. 

 But after being frozen, a great part of the starch disappears, and the particles which re 

 main are not more than a half or a quarter of their former size. I have not, however, 

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



