126 THE PHENOMENON OF 



cation of the cell happens in the vegetative sphere, the 

 cells increase in number by a succession of divisions 

 before the vegetative cycle closes with fructification ; but 

 the plant is incapable of keeping intimately connected the 

 generations of cells thus produced, of building- forth the 

 organism as a whole, in these divisions ; it breaks up 

 more or less completely into the individual cells, which 

 thus, although members of a definite cycle of vege- 

 tation, lead a separate individual life. We see that 

 which is completed by the higher plants in an orga- 

 nically connected series of cells, represented here by 

 an alternation of generations of unicellular vegetable 

 individuals.* It is therefore impossible to draw a 

 strict line between Unicellular and Multicellular plants 

 in this respect, since there exist numerous intermediate 

 stages leading from the most intimate union to total 

 separation. 



The completion of the contrast of growth and dif- 

 ferentiation of the organs does not always keep pace with 

 the simplicity or complexity of the tissue. Even among 

 the Unicellular Algae, most strictly so called, we find the 

 general opposition of growth of the plant expressed more 

 or less distinctly in the unicellular individual ; in fact 

 we find that the very fundamental organs of the plant, 

 stem, leaf, and root may be represented with more or 

 less evident distinctness by parts of one and the same 

 cell. The graduated succession which we detect, in this 

 respect, among the Unicellular AlgEe, is so well adapted 

 to enlarge the ordinary conception of the cell, that we 

 cannot omit a brief examination of it here. 



The simplest condition of the unicellular plant would 



and Tlmret, the originally simple spore of Fucns canaliculatus breaks up 

 into two, that of F. nodosus into four, of F. serratus and vesiculosus (doubt- 

 less by repetition of division) into eight spores. (Vide Deeaisne and Thuret, 

 ' Sur les Antheridies et les Spores de quelques Fucus,' ' Ann. des Sc. nat.,' 

 1845. 



* Here refer the Diatomaoese, Desmidiaceae, and most of the Palmellacete. 

 For the course of the generations of the first, see Thwaites ' JFurther Observa- 

 tions on the Diatomaoese,' ('Ann. and Mag. of Nat. Hist.,' 1848, sec. 

 ser. i, 161.) -, 



