i88 
The Ohio Naturalist. 
[Vol. VII, No. 8, 
EVERGREEN PLANTS OF OHIO. 
Grace T. Earl. 
The length of life of leaves varies greatly. The leaves of the 
so-called evergreen trees and shrubs persist through the winter 
without much apparent change. The leaves of some evergreens 
persist through only one year, falling off as soon as those of the 
succeeding year have fully developed. In • some conifers the 
branches always bear leaves formed during several years, although 
the old leaves may be shed continually. 
The cuticle in some evergreen plants is so very highly devel¬ 
oped that the outer wall of the epidermal cells is many times 
thicker than the inner wall, as in the case of Pines and Christmas 
Holly. The same is true of evergreen parasites, as, for example, 
the Mistletoe which lives epiphytically on the bark of trees; and 
generally the majority of the succulent plants also possess epi¬ 
dermal cells with very thick outer walls. In many plants the 
cuticular layers are of equal thickness over the whole surface 
of the leaf and this is common especially in the case of the smooth, 
shiny, leathery leaves. But the formation of a thick cuticle on 
the epidermis is not a peculiarity of evergreen leaves, for there 
are some in which the outer wall of the epidermal cells is not at 
all or only very slightly thicker than the inner. In various 
evergreens anthocvan is developed which causes the leaves to 
take on a red color at the approach of cold weather, as is the case 
in some species of Sedum. 
Evergreen leaves must have special adaptations to overcome 
the effects of freezing since their delicate tissues are exposed to 
very low temperatures in our latitude. At a freezing temperature 
vapor is given off from the protoplasm into the inter-cellular 
spaces where ice crystals are formed. The frozen tissue shows 
between the ice masses dense areas composed of the collapsed 
cell-walls packed closely together. This condition is very notice¬ 
able in frozen buds and the bark of hardy trees, and sometimes the 
cells appear entirely disorganized, but on thawing they again 
expand by taking up water and the normal turgidity is restored. 
Some evergreen leaves are so organized that they are able to 
survive the periods of drought or frost of one or even several 
years without injury. 
A number of kinds of rosettes are evergreen or nearly so in 
Ohio. Some biennial rosettes as the Verbascums do not freeze 
entirely even during the coldest weather. Among the more hardy 
pereninal rosettes may be mentioned the species of Senecio, Tar¬ 
axacum, and Achillea. Such plants as Poa pratensis, Lonicera 
japonica, and Nepeta cataria may be included among the plants 
