8o THE EVOLUTIONIST AT LARGE. 



atmosphere around, and is separated by the 

 sunlight acting in the leaves. There it mixes 

 with small quantities of hydrogen and nitro- 

 gen brought by the roots from soil and water ; 

 and the starches or other bodies thus formed 

 are then conveyed by the sap to the places 

 where they will be required in the economy 

 of the plant system. That is the all-import- 

 ant fact in vegetable physiology, just as the 

 digestion and assimilation of food and the 

 circulation of the blood are in our own bodies. 

 The arum, like the grain of wheat, has 

 only a single seed-leaf ; whereas the pea, as 

 we all know, has two. This is the most fun- 

 damental difference among flowering plants, 

 as it points back to an early and deep-seated 

 mode of growth, about which they must have 

 split off from one another millions of years 

 ago. All the one-lobed plants grow with 

 stems like grasses or bamboos, formed by 

 single leaves enclosing another ; all the 

 double-lobed plants grow with stems like an 

 oak, formed of concentric layers from within 



