42 THE ELEMENTARY STRUCTURE OP PLANTS. 



and shrubs, and some part of almost all ordinary herbaceous plants, 

 is wanting in Mosses and plants of still lower grades, such as 

 Lichens, Sea-weeds, and Fungi. That is, in the latter there is no 

 formation corresponding to the wood of higher plants, although 

 many of them exhibit, at least in certain parts, cells more or lesa 

 elongated, or even drawn out into tubes or hollow fibres of greater 

 length and tenuity than are those of ordinary wood ; such, for 

 instance, as the interlaced fibrous tissue of Lichens (Fig. 25). 

 Nor, on the other hand, does the proper wood of trees (except ii» 

 the Pine family) consist entirely of what is named woody tissue, 

 but has some other sorts variously intermingled with it. Indeed, 

 there are some trees whose wood is almost entirely composed 

 of true parenchyma, or of large dotted cells ; while in stone-fruits, 

 and many like cases, common parenchymatous cells acquire by in- 

 ternal deposit (41) a ligneous consistence, and even greater hardness 

 than ordinary wood (39). Nevertheless, the principal and charac- 

 teristic component of wood in general is thick-walled prosenchyma. 

 So that this takes the name of woody tissue even in the bark and 

 leaves, as well as in the trunk. Fig. 32 represents some of the 

 various elements of the wood of the Plane-tree. And Fig. 46 ex- 

 hibits three or four wood-cells from the same tree, more highly 

 magnified; the two right-hand ones cut through lengthwise, and 

 one of these, at the upper end, with a piece of another, also cut 

 across, to show the thickness of the walls. 



54. This and the following figures likewise show how the wood- 

 cells are as it were spliced together, overlapping one another by 

 their tapering ends. Forming wood consists of oblong or prismatic 

 cells, with their ends nearly square or merely oblique: as these 

 young cells lengthen, the ends become more oblique, and push by 

 each other, or become wedged together. The wood-cells repre- 

 sented in Fig. 46 are about gVijij of an inch in diameter. Those of 

 our Linden or Bass-wood (a few of which are shown in Fig. 50, 51) 

 are rather larger, but not more than y^g- of an inch in diameter.* 

 Their size varies in different plants almost as much as ordinary cells 

 do, but they are usually much smaller than parenchyma, especially 

 in herbaceous plants. Perhaps the largest are found in the Pine 

 family, where they are of a peculiar sort, and are often as much 



* Lindley states that the woody tubes of the Linden are as much as -jl^ of 

 an inch in diameter ; but I find none of anything like this size. 



