CHAPTER: fi 
VESSELS AND THE “BUNDLES”: WOOD, 
CAMBIUM, AND BAST 
WE may now turn to the higher plants and consider 
their more elaborate factories. The bulk of the living 
part of such plants still consists of our ordinary cells, 
but we have now, so to speak, three elements to study, 
which correspond in a way to our own skin, flesh, and 
bones. The flesh we discussed in the last chapter, but 
a few words may be fairly in place about the skin. All 
plants that have anything like a complex organisation, 
ze. all plants that rise above the single cell, or the single 
layer of cells, begin to feel the want of a skin, and they 
clothe themselves with a single layer of cells, usually 
colourless, and fitting closely together all over the plant. 
This skin you can tear off for yourselves from almost any 
leaf, and you will see that it is a transparent membrane 
covering the green chlorophyll cells beneath. It seems 
to be, as I said, continuous, but if you 
look at it with a low-power microscope 
you will see there are small holes or 
mouths in it (stomata). These serve 
the purpose of the pores in our own 
skin to some extent, for they allow the 
water to evaporate when the plant on 
STOM 4. rare occasions has more than it wants, 
16 
