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president’s address. 
closed ends of the fibro-vascular bundles of the veins, when it 
appears as drops fringing the margin of the leaf. 
The power of resistance by plants to very low temperatures is 
entirely dependent upon the amount of water they contain. The 
leaves of evergreens hold very little water during winter, and 
winter buds at the same time possess only a minimum quantity, 
whilst they are well protected by impervious scales, which act as 
useful shields, but every plant has a minimum of temperature 
below which it would be killed. When in America, I was told by 
a peach farmer that peach trees in the open orchard would with- 
stand a temperature of 5 degrees below zero ; but below that, 
many would be killed. Now I think that peach trees here in 
England in the open would succumb long before that temperature 
were reached ; and the explanation is, no doubt, that the winter 
buds and stems are much more desiccated there in autumn, than 
they are here in our moister climate. So long as seeds and buds 
are perfectly dry, they can withstand the effects of very low tem- 
peratures ; but as soon as they absorb moisture and growth 
commences, the young cells have no power of protecting themselves 
and the leaves perish at the first frost. Hardy succulent plants, 
however, have rather a hard time of it, but some of them possess 
certain protective means by which their destruction is prevented. 
It is interesting to note how such leaves as those of the dahlia, 
artichoke, etc., are killed by the first frost, whilst those of some 
equally succulent kind take no harm, and are able to withstand a 
prolonged period of frost. As the cold increases contraction takes 
place, a portion of the water of the cell sap escapes through the 
cell walls into the intercellular spaces, and freezes in crystals on 
the outside of the cell wall ; the other portion which is in close 
combination w r ith the cell contents — water of imbibition — does not 
freeze, at least not until a very low temperature is reached. On 
returning to a normal condition again, if the thaw be gradual, the 
water that has frozen on the outside of the cells slowly diffuses 
back, and they recover their turgidity ; but should the thaw be 
rapid, the water will be prevented from slowly diffusing, and as a 
consequence the leaf tissue will become broken up and the leaf 
