ITS FLORA. 33 



simple aggregation of cells, as in the sea-weeds and lichens, to 

 the more complex fronds of the ferns and clu~b-mosses ; from 

 these to the parallel-nerved leaves of the grasses and palms ; 

 and from these again to the reticulated and more highly 

 organised venation of the leaves of the flowering shrubs 

 and true timber-trees. He further finds that, while the 

 leaf is produced by the development of the cell, all the 

 other organs of the plant are but modifications of the leaf 

 that the stem and branches are elaborated from the suc- 

 cessive growths of leaves, that the petals of the flower are 

 but modifications of the same organ for a special purpose, 

 that the fruit is but a specialised combination of leaves, and 

 that the seed itself consists of a leaf or leaves folded up 

 and protected for the return of those conditions of heat and 

 moisture necessary to its starting again into life and verdure, 

 to perform the same round of development and reproduc- 

 tion. How this cell, or globule of matter, should become 

 vivified how it should be capable, under certain conditions 

 of heat, light, and moisture, of being reproduced indefin- 

 itely into some determinate form as a leaf, and how these 

 leaves or leaf-like organs should be persistently maintained, 

 each in its own distinctive type throughout the great 

 categories of the vegetable kingdom are problems which 

 science cannot solve. We know, however, the facts and 

 the order of their occurrence. We perceive the expres- 

 sion of a prescient plan ; that plan we endeavour to inter- 

 pret. Everywhere purpose and design are manifest ; into 

 the motives of the Designer we may not inquire. The 

 secondary we may discover : to the primary we can only 

 appeal. 



Founding on this great principle of cell and leaf develop- 

 ment, the botanist traces its elaboration in the different 

 races of plants, and regards those which manifest little more 

 than a repetition of the same parts as of lower organisation 



