34 THE PRESENT. 



than those in which the leaf is metamorphosed into various 

 organs, each organ having a special function to perform in 

 the plant's growth and perfection. The higher, therefore, 

 that a plant is in the scale of being, the more specialised its 

 organisation ; that is, instead of all the functions or several 

 of its functions being performed by the same organ, each 

 function is performed by an organ specially devoted to it. 

 It is thus that the fern is regarded higher than the sea- 

 weed ; the palm higher than the fern ; and the oak than 

 the palm. In ranking plants as " higher" and "lower," 

 the botanist by no means asserts that the one is less fitted 

 than the other for its purpose in creation. All that he 

 affirms and common-sense homologates the affirmation 

 is, that the lichen, composed of a mere congeries of cells, 

 and increasing by a mere homogeneous development of 

 these cells, is a less highly organised structure than the 

 timber- tree, in which is elaborated a variety of tissues, which 

 is increased by leaf-growth, and whose reproduction is pro- 

 vided for by a complicated process of flowering and fructifi- 

 cation. Aware of these distinctions, and knowing the per- 

 sistency of nature in her modes of operation, we can 

 determine the relative positions not merely of the plants 

 that now adorn the various regions of the earth, but of 

 those that existed during the successive epochs of her by- 

 gone history. As a region of shrubs and timber-trees is 

 said to enjoy a higher flora than a region of ferns and club- 

 mosses, so do the reticulated leaves and concentric woody 

 layers, found fossil in a recent rock- system, give indication 

 of a higher physiological value than the parallel-veined 

 leaves and vascular-bundled steins of some earlier forma- 

 tion. It is thus that we arrive, in general terms, at the 

 great truths of vital progress a leaf, a stem, the disposi- 

 tion of a branch, or the structure of a fruit, affording such 

 evidence to the palaeontologist as the flint arrow-head, the 



