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collections of trees. There are, for instance, scores of oaks 

 at Kew of one and the same species, whose leaves vary 

 from small and slender cut ones to huge and bluntly lobed 

 ones, and all shades in between. The fronds eclipse the 

 leaves in versatility, and especially in their power of 

 sporting into those tasselled tips, examples of which have 

 been found in a large number of species. No leaf proper 

 does this ; the faculty seems to be correlated with that 

 peculiar mode of growth which characterises all fronds, 

 i.e. tip growth. The frond and all its parts develop by 

 continued growth of all the tips, while the leaf, as we have 

 seen, develops differently, and it would appear that with 

 the tasselled varieties, the developing tips multiply their 

 terminal cells at a certain stage, and, these continuing 

 their growth, the result is the eventual formation of a 

 tasselled instead of a normal point. Leaves and fronds 

 both display very different forms of venation, i.e. of the 

 ribs and veins which stiffen them, and form their channels 

 of sap supply. 



Veining of Leaves. 



In flowering plants the two great families of exogens 

 and endogens, monocotyledons and dicotyledons, or to 

 put it popularly, those which tend to form annual rings of 

 wood and have two primary leaves produced from the 

 seed, and those which form no such rings, and have only 

 one primary leaf, are also roughly differentiated by the 

 vein system being netted in the first case, and on a 

 straight line system in the second. Thus we cannot tear 

 an oak leaf straight from top to bottom, as we can a lily 

 or a grass leaf. In ferns we have two systems, netted and 

 non-netted, but no longitudinal system, and it is a peculiar 

 fact that the tasselling appears to be a matter of some 

 difficulty with netted ferns as compared with non-netted, 

 since examples are not so common, and when found are 

 not so thoroughbred, as we may see in the crested Wood- 



