72 MINUTE MARVELS OF NATURE 



a section of a portion of the leaf of the maize 

 or Indian corn, showing that the leaf-blades ot 

 plants which are widely removed from each 

 other in the vegetable kingdom are still only 

 variations of the same plan to fulfil the same 

 purpose, merely specialised in the division of 

 labour to meet the particular ends of the plant. 

 This example may be taken as a type of the 

 leaf structure peculiar to the "monocotyledons," 

 the grasses, lilies, &c., in the same way that 

 the laurel, sunflower, and water-lily were types 

 of " dicotyledons." If we take one of the 

 smaller plants, such as mosses, which are neither 

 " dicotyledons," i.e., plants whose seeds throw 

 out a double leaf, nor "monocotyledons," which 

 send out a single shoot, like a blade of grass 

 plants, indeed, which have no seed-leaves at 

 all, because they have no proper seeds we find 

 that there is seldom need to make a section 

 of a leaf, because the leaves of most mosses 

 consist of a single layer only, of cells, which 

 are generally simple as shown in Fig. 49. It 

 will be seen that these leaves have no mid-rib, 

 although there are some mosses in which this 

 differentiation of tissue first begins to appear 

 with a few thick-walled cells or rudimentary 

 vascular strands which constitute the first step 

 towards the evolution of the mid-rib, so highly 



