HOW PLANTS EAT. 43 



have access to sunshine ; they must also be sup- 

 ported or held in place so as to catch it. For 

 this parpose they have need of what we may 

 venture to describe as foliar architecture. This 

 architecture takes the form of ribs or beams of 

 harder material, which ramify through and raise 

 aloft the softer and actively living cell-stuff. 

 They are, as it were, the skeleton or framework 

 of the leaf ; and in what are commonly known 

 as " skeleton leaves " the living cell-stuff between 

 has been rotted away, so as to display this harder 

 underlying skeleton or framework. It is com- 

 posed of specially hardened, lengthened, and 

 strengthened cells, and is intended, not only to 

 do certain living work in the plant (as we shall 

 see hereafter), but also to form a supporting 

 scaffolding. The material of which ribs or 

 beams are composed is called ** vascular tissue" 

 — a not very well chosen name, as this material 

 has only a slight analogy to what is called the 

 vascular system (or network of blood-vessels) in 

 an animal body. It is much more like the bony 

 skeleton. Similarly, the ribs themselves are 

 usually called veins — a very bad name again, 

 as they are much more like the bones of a wing 

 or hand ; they are mainly there for support, as 

 a bony or wooden framework, though they also 

 act for the conveyance of sap or water. 



And now we are in a position to begin to 

 understand the various shapes of leaves as we 

 see them in nature. They depend most of aP. 

 upon certain inherited types of ribs or so-called 

 veins, and these types are usually pretty constant 



