1 88 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 anthocyan 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. i\mong the more hard}' 

 pereninal rosettes may be mentioned the species of Senecio, Tar- 

 axacum, and Achillea. Such plants as Poa praiensis, Lonicera 

 japonica, and Nepeta cataria may l)c included among the plants 



