16 BRAUN, ON UNICELLULAR ALGiE. 



not less by geological than it is by morphological con- 

 siderations. 



Another division, lastly, of phanerogams, in which the 

 highest stage of the vegetable kingdom is reached, em- 

 braces all flowering plants which at the same time produce 

 true fruit — angiospermous anthophytes ; and in this section 

 the subdivision into monocotyledons and dicotyledons is of 

 secondary importance. 



In what way the vegetable kingdom, as far as concerns the 

 scale or gradation of evolution, agrees in general with an indi- 

 vidual plant, may, with respect to the first commencement 

 of the lowest step, be so specifically compared, that a law of 

 analogy is clearly apparent in the accordance of the lowest 

 plants with the lowest state of a higher plant. It is evident 

 that every plant commences in a solitary and simple cell, 

 either a spore or an embryo sac ; it is clear also that the suc- 

 ceeding (succedaneous) generation originates in a simple cell 

 (embryonic vesicle) ; the vegetable kingdom presents an ana- 

 logous commencement ; its lowest members are plants unicel- 

 lular throughout their life — plants, that is to say, constituted 

 of a single cell persistent through the whole period of evolu- 

 tion, and performing all the vital functions. The existence 

 of unicellular plants of this kind has been long and frequently 

 shown, though demonstrated by imperfectly known, and for 

 the most part erroneous examples, until Nageli laid a new 

 foundation for the doctrine, in his careful illustrations of several 

 genera of unicellular Algce, and their classification according 

 to a new method. But the limits within which that expe- 

 rienced observer circumscribed the unicellular Aft/ce, appear 

 to the author too restricted, and scarcely such as should be 

 closely observed; a circiimstance which some have endea- 

 voured to turn to the disparagement of the doctrine itself, 

 going so far as wholly to deny the existence of unicellular 

 Alffce at all, or even as to declare that the proposed genera 

 were most of them the pi'imoi'dia merely of more perfect 

 Algce or of other plants, whilst others were said to be the ova 

 of animalcules. It is scarcely worth while to attempt the 

 refutation of these opinions, since they are unsupported by 

 arguments derived from accurate observation, and because all 

 who may enter with unprejudiced views into the vast domain 

 of the lowest Alga will be con\dnced that the truth is other- 

 wise. 



{To he continued^ 



