608 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



That a natural sj^stem has been evolved along lines resembling the ramifications 

 of a tree, which commenced with simply organized structures and terminated with 

 the most complex ones, finds a certain confirmation when the history of develop- 

 ment of the individual (ontogeny, from Cov, 6vtos, being; and yewaoj, to produce) is 

 compared with its position upon the phylogenetic tree. As we know, the greatest 

 of all flowering trees begins its existence as a single protoplasmic mass. This 

 surrounds itself with a cell- wall and increases in size and complexity at the expense 

 of nutriment derived from its environment. Gradually cells and tissues arise and 

 the young organism becomes segmented into an axis and appendages. These, again, 

 assume the most varied forms corresponding to a subdivision of labour. Ultimately 

 the uppermost and last-produced members of the plant are transformed into flowers 

 and fruits. It is thought that, just as a plant is gradually difierentiated in this way 

 so have all plants undergone a similar transformation, step by step. The egg-cell, 

 the starting-point of the individual, may be compared to a Myxomycete, the cell- 

 complex which arises from the egg-cell after fertilization to a Thallophyte, the 

 segmented axis and appendages of the seedling to a Vascular Cryptogam, and the 

 complete plant-body, finally, to a Flowering Plant. 



This comparison, like so many others which captivated the imaginative faculties 

 in the days of the speculations of nature-philosophy, has found many adherents; 

 indeed, it has served as dogma and guiding light in many investigations. But it 

 is difficult to harmonize it with other theories well-proved by experience. The 

 main burden of this comparison (known as the " Recapitulation-theory ") is that 

 the vegetable kingdom as a whole has undergone a developmental history and 

 transformation resembling that of a single member of the group of Flowering 

 Plants. But first it must be asked, what is the meaning of metamorphosis in the 

 individual, and what object has been attained by it? Though the actual processes 

 taking place in the living protoplasm in metamorphosis are unknown, this much 

 seems certain: That these changes occur along lines sufficiently well indicated; 

 that the fashioning of the successive stages of any given species is accomplished 

 according to a definite plan; that external influences, such as soil and climate, do 

 not permanently afiect this plan; and that consequently the plan of construction 

 of these successively appearing stages is laid down in the protoplasm itself. The 

 ultimate object of metamorphosis in plants is the production of fruit; and with 

 the formation of an ovary the metamorphosis ends, the fertilized egg-cell beginning 

 the metamorphosis all over again, i.e. it is the starting-point of a series of trans- 

 formations along identical lines. And this applies equally to the Apple-tree and 

 to the Palm, to the Pine, the Horse-tail, the Moss, the Bladder-wrack, Stonewort, to 

 the Mould, and to the simplest of green AlgaB. Only in the last-named forms are 

 the intermediate stages fewer than in the first-named. But it will hardly be sug- 

 gested that the latter have not on this account attained the end in view. Simple 

 plants whose fertilization and fruit-formation is accomplished under water, whether 

 it be on inundated land, in the mud of a river, or at the bottom of a lake, attain 

 this end without a complex metamorphosis of petals and stamens; whilst many 



