552 FREEZING AND BURNING. 



meadows they are only to be found at a depth three or four times as great. The 

 position of the tuberous roots of many orchids, and of the corms of the Meadow 

 Saffron (Colchicum autumnale) may be actually used as marks to indicate how 

 deeply in a given neighbourhood the ground is frozen, for these occur imbedded 

 just at that depth to which the winter frost fails to penetrate. 



The same thing is also observed in aquatic plants. In the still waters of lakes 

 and ponds the plants bodily withdraw before the advancing cold of winter, and an 

 actual retreat into the depths takes place. The Water Soldier (Stratiotes aloides) 

 sinks down before the commencement of winter to the bottom of the lake, where 

 it scarcely ever freezes; it passes the winter there, and does not rise again to the 

 surface till the following spring. Potamogeton crispy^, figured above, produces 

 late in the autumn, near the surface of the water, shoots possessing short leaves 

 which are detached from the old stem before the uppermost layer of water is frozen. 

 These sink into the depths, and bore their way into the mud by their pointed lower 

 extremities. There, in their winter quarters, where there is never any formation 

 of ice, these sprouts are excellently protected against injury from excessive cold. 



Erect trees and shrubs, which rise up column-like above the earth, are little 

 affected by the presence or absence of a covering of snow upon the ground. 

 Generally the leaves have been already shed, after they have delivered up such 

 substances as they contained of value. The leafless branches and the next year's 

 buds indeed remain above the ground, being thus exposed to the winter cold, which 

 they must be capable of bearing without injury. The branches are covered with a 

 tough and compact investment; and it would seem as if such a covering would be 

 able to protect the portion clothed by it against cold better than a mere epidermis. 

 For a very short period of cold weather such may be the case, but for a longer 

 period even the thickest coat would be unable to keep the cold from the covered 

 portions, just as little m fact as the bark on old boughs and trunks. In long- 

 continued winters, with uninterrupted severe cold weather, the interior of the 

 branches and trunks assumes the temperature of the environment, and it depends 

 entirely upon the resisting capacity of the protoplasm whether the cooling is fatal 

 or not. From various appearances it may be concluded that this resisting capacity 

 is greater the better the opportunity afforded to the protoplasm of suitably preparing 

 itself in the foregoing summer and autumn. If the summer was warm, and the 

 autumn mild, if the advent of the first frost was much retarded, and the plant had 

 time to become a chrysalis slowly, in preparation for the winter, then the branches 

 do not freeze dead; but if the summer was cold and wet, and frosts appeared early 

 in autumn, if the water of imbibition was not removed at the right time, and the 

 wood, as gardeners say, is not " ripened", then a tolerably severe winter may result 

 in the death of the branch, of the same branch, indeed, which perhaps in previous 

 years survived without injury much greater cold. 



Accordingly we always come back to this, that the freezing of a plant to death, 

 or not, depends upon whether or not the condition of the protoplasm is such that 

 its molecular constitution becomes permanently disorganized in consequence of tho 



