Effects of Frost on Plants. — Q7 
tenuity, but in which the motion of the latex may be seen beau- 
tifully with the one-eighth of an inch object-glass of an achro- 
matic microscope. Upon being thawed after freezing, all this 
apparatus is found reduced to some misshapen separate sacs of 
fine grumous 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 microscope ; for if a stem of a Ficus elastica, 
or an Euphorbia, or any such plant, which discharges an abun- 
dance 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 phenomena : 
“1. A distension of the cellular succulent parts, often attended 
by laceration, and always by a destruction of their irritability. 
n expulsion of air from the aeriferous passages and cells, 
‘¢3. An introduction of air, either expelled from the air-passa- 
ges or disengaged by the decomposition* of water, into parts in- 
tended exclusively to contain fluid. 
“4, A chemical decomposition of the tissue and its contents, 
especially the chlorophyll. 
“5, A destruction of the vitality of the latex, and a stoppage 
of the action of its vessels. 
«*§, An obstruction of the interior of the tubes of pleurenchy- 
ma (woody fibre) by the distension of their sides. 
‘‘ These phenomena may be considered in part mechanical, in 
part chemical, and in part vital. The two latter are beyond our 
control. ..* -*.% The mechanical action of frost may, how- 
ever, undoubtedly be guarded against to a great extent. It is 
well known that the same plant growing in a dry climate, or ina 
dry soil, or in a situation thoroughly drained from water during 
winter, will resist much more cold than if cultivated in a damp 
climate, or in wet soil, or ina place affected by water during 
winter. Whatever tends to render tissue moist will increase its 
wer of conducting heat, and consequently augment the sus- 
ceptibility of plants to the influence of frost ; and whatever tends 
er disengaged from the water, which held it in solution, during the act 
of oe AG: 
