ee mc es 
118 MISSOURI BOTANICAL GARDEN. 
the Coniferae. The new growths at this time were just 
started, and they were entirely killed. Of course the old 
growth of leaves, even if frozen, did not show any effects. 
In Broussonetia papyrifera, Catalpa bignonioides, Paul- 
ownia imperialis, the. killing was perhaps the most com- 
plete of all the trees and shrubs observed, in the case of 
the latter even extending into the old wood itself. Mag- 
nolia grandiflora is not hardy in this section, and only 
thrives when protected in winter. This protection had, of 
course, been removed and the new growths, as might have 
been expected, caught the full force of the freeze. It, how- 
ever, responded well, and growth during the season was 
nearly normal. Paulownia, in the season from April 24 
to the time of the first fall frost, October 28, made growths 
of ten to twelve feet. It, too, is but half hardy and freezes 
back a little nearly every winter and, strangely, after 
having passed the winter without freezing back, it did so, 
in some cases, as a result of the spring freeze, as evidenced 
by the appearance of the buds on the old wood. This is 
probably owing to the fact that growing tissue is much 
more susceptible to cold than is older tissue. 
In recording the effects of the freeze on the many trees 
and shrubs of the list, several reasons have suggested them- 
selves that partially explain why some leaves froze and 
why some did not. (a) Perhaps the most suggestive 
answer is the one of sap density. It is a well-known law 
of physics that solutions of different density have different 
freezing points. The freezing point for water being 32°F., 
any aqueous solutions, such as plant juices or saps, will 
have freezing points below that of pure water. We may 
suppose, then, that differences of sap density may determine 
the relative resistance to frost or freezing. The answer to 
this suggestion will occupy the second part of this paper 
and will not be taken up further here. (b) The opening 
of the buds, and the development of shoots and leaves, 
extends through a period of several weeks. It is rather 
interesting to note that those plants unaffected by the frost 
aan 
