Butters and RoscndaJil: effects of frost. 155 



vegetation in general was of this type. (2). During the very 

 severe freezing of April 23rd succulent parts of plants froze 

 absolutely solid and became very brittle. In this condition many 

 of them were snapped off by the high wind. 



The amount of mechanical damage in the case of any plant 

 was quite independent of the actual frost-hardiness of the pro- 

 toplasm. Of course it was most conspicuous in those plants 

 which received comparatively little direct injury from the low 

 temperature. Both sorts of mechanical injury, particularly that 

 of the second kind, were much greater in exposed than in protected 

 situations. The lilac bush (Fig. 1) exhibits the effect of direct 

 exposure to the wind during the morning of April 23rd. Scarcely 

 a leaf or young twig remained alive on the windward (northerly) 

 side of the bush. 



Direct Eifects of Lozu Temperature. Relative Hardiness of 

 Different Species and Different Parts of Plants. — As was to be 

 expected, different plants showed to very different degrees the 

 power of surviving the low temperature. Alany had all their 

 new growth killed or severely injured by the first frost. These 

 included about 24 per cent, of the native trees and shrubs (See 

 Table I). With these were some exotic herbaceous plants but 

 almost no native herbs. A larger number escaped with little in- 

 jury from the first frost but were severely injured by the sec- 

 ond — about 30 per cent, of native woody plants (See Table II), 

 and a somewhat smaller proportion of native herbaceous vege- 

 tation. In many cases the mechanical damage during the sec- 

 ond frost was so great that it was impossible to determine whether 

 or not the protoplasm of the plant was frost-hardy to the extent 

 of enduring the temperatures that then obtained. It appears evi- 

 dent, however, that irrespective of this mechanical injury many 

 plants are able to endure 2.5 degrees (C.) of freezing but are 

 killed or severely injured by an additional five degrees. ]\Iany 

 plants showed comparatively few ill effects resulting- directly from 

 the cold. In about 10 per cent, of the woody plants examined 

 (See Table III), and fully 50 per cent, of the native herbs, there 

 was no effect visible a few days after the frost, despite the fact that 

 they were in active growth at the time of the frost.* 



