THE YOUNG NATURALIST. 



267 



tematic classification of plants, as they 

 afford a ready means of referring a 

 plant to one or other of the two great 

 divisions of flowering plants. Thus 

 in Dicotyledons the veins branch and 

 run into each other, forming a regular 

 network, which is so beautiful in skel- 

 etonised leaves : this is known as retic- 

 ulate venation, and is characteristic 

 of all our native forest trees. In 

 Monocotyledons, such as grasses and 

 lilies, the veins run parallel with each 

 other from the base to the apex of the 

 leaf, scarcely, if at all, branching. 

 Such leaves are usually long and nar- 

 row, and the parts of the flower 

 are in multiplies of three, in ferns the 

 veins branch only in a forked manner. 

 In reticulate venation there are two 

 types, both of which are equally com- 

 mon, and give rise to two distinct 

 classes of leaves. In the one there is 

 a central well marked vein which runs 

 from the base to the apex, giving off 

 regularly on each side alternately 

 secondary veins, running to the 

 margin, feather-fashion, hence called 

 penni-nerved. This type is beautifully 

 shown in the sweet chestnut often 

 planted in parks, but the beech will 

 furnish a familiar example. When 

 such leaves become compound they are 

 called pinnate, as the ash, elder or 

 rose. In the other type the veins 

 radiate from the top of the petiole, 

 fan fashion, or like the fingers of the 

 band; so they are called palmi-nerved. 



as in geraniums, sycamores, ivy. When 

 this type becomes compound there is 

 invariably an odd leaflet, thus three in 

 clover and laburnum, five in bramble 

 or cinque foil, seven or nine in horse- 

 chestnut. Generally longish leaves are 

 penni-nerved, whilst roundish leaves 

 are palmi-nerved. The variety in 

 shape of leaves is endless, no two 

 blades of grass being exactly alike, 

 from the orbicular penny wort and 

 shield-like nasturtium, to the sword- 

 like leaves of the iris, or the needles 

 of firs. Their substance or texture is 

 as varied, from the juicy fleshy leaves 

 of the cabbage to the tough leathery 

 ivy or holly. Their surface covering 

 is equally diversified from the smooth 

 wallflower and polished laurel, to the 

 flannelly mullein or bristly thistle ; 

 and in range of size we have the huge 

 expanse of the butterbur two feet in 

 diameter, to the minute scales of furze 

 or heath., 



Functionally leaves may be grouped 

 into four divisions, scale or covering 

 leaves, nutritive or foliage leaves, floral 

 or reproductive leaves, and cotyled- 

 onary or seed leaves. The first of 

 these are well shown in those scales 

 which invest buds during winter, 

 protecting the tender growing parts 

 from the frost and rain, and thrown 

 off in spring to allow of expansion and 

 growth, the membraneous scaly coat 

 of an onion or tulip are of this 

 character, as are also the chaffy glumes 



