THEIR FRUCTIFICATION AND MOVEMENT. 211 



mode of forming fruit in both these families, Desmidiece 

 and Diatomaceae, which is also the mode among un- 

 doubted Algse, is by the coupling together of two cells 

 or frustules, when a passage is gradually formed between 

 them, through which the contents of one cell are dis- 

 charged into the other, where a dense mass of granular 

 matter collects, which at length solidifies into a spore 

 and bursts through the walls of the cell. As such a 

 process of reproduction is more analogous to what takes 

 place in the vegetable than in the animal kingdom, 

 naturalists seem now generally agreed to class them 

 with vegetables. The advocates for their animal nature 

 appeal to certain motions, having the character of 

 voluntary motion, observed in many species. Thus 

 Bacillaria paradoxa alternately propels its frustules 

 forward and draws them back, opening out the filament 

 of which the compound body consists into a straight 

 line, and contracting it again into a narrow compass. 

 This little plant resembles a pack of narrow cards, joined 

 together at one of the angles of their smaller end : when 

 extended they are ranged in a straight line, and when 

 contracted they are folded back on each other and lie as 

 if in a pack. It is highly curious to watch the regular 

 manner in which this motion is continued. Some of 

 the other species have movements of a similar character, 

 but many have not been observed in motion : and such 

 motions as are seen, more resemble the regulated move- 

 ment of a machine than the voluntary changes of place 

 which animals exhibit. No doubt it is difficult, perhaps 

 impossible, to draw a 1'igid line between the irritability 

 of a vegetable and the muscular and nervous contractions 



