490 



PEACTICAL BOTANY 



The various strata or stories of vegetation in a forest are 

 usually arranged somewhat in the order of their light require- 

 ments, the plants most tolerant of shade at the bottom and 

 the most intolerant species at the top. Thus in an open 

 forest composed mainly of white pines mixed with a few 



other conifers and some 



deciduous trees, in New 

 England, we may find some 

 such assemblage as this : 

 close to the ground vari- 

 ous species of mosses, the 

 most consjDicuous being the 

 pigeon-wheat moss (Polyt- 

 richufn). Rising but little 

 above the mosses are one 

 or two species of " ground 

 pine," or "Christmas ever- 

 green" (^Lycopvdlum, Fig. 

 245). ^lingled with these 

 are many herbaceous spe- 

 cies, or very small under- 

 shrubs representing the 

 seed plants, all shade-loving 

 species, such as rattlesnake 

 plantain,! " wild lily of the 

 valley, "2 chickweed, win- 

 tergreen,^ common wood 

 sorrel,"" prince's pine,^ shin- 

 leaf,^ partridge berry,''' and 

 rattlesnake-weed.^ Above 

 these, if the woods are young, grow such larger shrubs and 

 small trees as Juneberry,'' blueberry,!^ and gray birch.^i l\Iixed 

 with these are young spruces and perhaps hemlocks. Only 



1 aoodijera. 2 Mahinlhmium. 8 Trientalis. * Oxalis Acetosella. 



^ Ohimaphila. ^ Pyrola. ^ ilitrhella. ^ Hieracium. ^ Amelancliier. 



1° Vaccinium vacillans. n Betula populifolia. 



Fig. 369. An air plant (Ti/taiidsia) of the 



Pineapple family- 

 Living as an epiphyte, but having numerous 

 roots, it is intermediate in habit between 

 the common pineapple (Fig. 283), which 

 grows rooted in the earth, and the Spanish 

 moss (Fig. 368), which is rootless and hangs 

 suspended from the bark of trees. Photo- 

 graph by Robert Cameron 



