A WIDE WORLD OF PLANT-LIFE 41 



A third distinction helps to mark these Subdivisions 

 as apart each from the other. 



With a Two-Cotyledon plant, if we study the leaf 

 carefully, we shall nearly always find its markings its 

 ribs and veins to be netted. There may be a main rib 

 running up the middle, and there will be many lesser 

 ribs or veins branching off sideways towards the edges. 

 When we try to tear this leaf, it will not tear straight, 

 but only in a jagged way along the branching side-ribs. 

 This can be seen with an Oak-leaf or a leaf from a 

 Rose-tree. 



But if we get a Lily-of-the- Valley leaf we shall at 

 once find that it is not netted or branched. A number 

 of long lines run all the way from the stalk to the leaf- 

 tip. And if we try to tear it, we shall see that it tears 

 smoothly down its full length. It is the same with 

 other Mono-cotyledon plants. 



And yet again a fourth difference exists between 

 these two big Subdivisions. 



If an Oak or an Elm is cut down, and we look at the 

 cut end, we may notice many lines running round, circle 

 within circle. These lines show the age of the tree. 

 Each year a fresh growth or layer takes place, between 

 the outer wood and the bark; and so the trunk gets 

 steadily larger year by year. That is the way in which 

 Di-cotyledon plants grow (see page 74). 



But the Mono-cotyledon plants increase in quite 

 another fashion. 



They do not grow by added outer layers. The wood 

 of a Palm-tree, for instance, when cut down shows no 

 circles, Jt does not increase by layer added to layer. 



