130 THE PHENOMENON OF 



which developes itself into the form of stem, root, and 

 leaf. The origin of organs of distinct kinds, which is 

 connected in the higher plants with a very complicated 

 multiplicity in the cell-formation, appears here to be 

 attained simply by development of one and the same cell, 

 separating itself into different directions of growth. 



The simplest plants with a many-celled cycle of vegeta- 

 tion, whether this be connected or broken up into con- 

 stituent members, stand far behind the plants with a 

 unicellular cycle last considered, in regard to organic 

 differentiation. In this series again, nature ascends by a 

 scale of different types, from a minimum of contrast in 

 growth, to a progressively more distinct realization of the 

 various directions of formation. That W'hich was attained 

 in the former cases through the differentiation of the 

 individual cell, without isolation of its parts one from 

 another, is here reached in the most manifold gradations 

 through the formation of cells differing among themselves, 

 this happening either merely by a difference in the gene- 

 rations of cells, or by a different character of the cells of 

 the same generation. The distinctions occurring here 

 may relate either to the mode of origin of the cells 

 (combined or free formation), to the generative capability 

 (permanent cells and mother-cells), or to the mode of final 

 development (predominant growth in one or other direc- 

 tion, the different shaping of the contents and of the walls). 

 Thus arises an infinite variety in the genealogy, arrange- 

 ment and final development of cells, which becomes the 

 more difficult to trace the higher we ascend in the vege- 

 table kingdom. I confine myself to a few indications 

 from the lower groups of the vegetable kingdom, especially 

 from the Algae, the deep study of which appears the more 

 important the more fully the science becomes conscious 

 of its object to penetrate into the regulated course of 

 development of vegetable structures in all their infinite 

 complications. 



The simplest conditions are exhibited by those plants 

 in which all the generations of cells, except the transition- 



