IN THE VEGETABLE KINGDOM. 23 



rudimentary forms in which the process of conjugation pre- 

 vails. All these species may be considered as unicellular ; 

 for though the cells are not in every case isolated, they have 

 always the capacity of maintaining an independent life, 

 when by any means they are separated from each other. 



When in connection with each other, the cells are ar- 

 ranged in various fashions ; in some Palmellese they are 

 embedded in a gelatinous matrix, in other cases they co- 

 here sidewise to form flat or bullate fronds, but in the ma- 

 jority they are connected in single file, in filaments simple 

 or branched according to the species. Except in Palmellese, 

 the cell wall becomes eventually a well-defined structure, 

 and consists of a layer of cellulose, lined by a film of an 

 albuminous nature, which is probably nothing more than 

 the outer pellicle of the protoplasmic contents. This in- 

 ternal protoplasm is generally coloured green occasionally 

 red by an accumulation of granules, termed endochrome. 



These Algae multiply in various ways. The smplest is by 

 a process of fission following on gemmation or cell-formation 

 the points at which the new cells are developed, and their 

 continued adhesion or otherwise, giving rise to the varied 

 forms of differently shaped fronds, or isolated cells. But 

 the most characteristic form of reproduction is by conjuga- 

 tion, already noticed as representing in a rudimentary way 

 that by the co-operation of the sexes. 



Conjugation has been observed in the confervoid genus 

 Zygnema and its allies, in most of the Desmidiese, and in 

 some species of Palmelleae and Diatomaceae.* The first step 

 in the process appears to be the rupture of the cell wall by 

 the growth of the contents, which then protrude as a se- 

 condary or pseudo-cell, surrounded by a pellicle formed 

 within the wall of the original cell. On coming in contact 



* For a notice of the recorded observations on the conjugation of the 

 Diatomaceae, see the Notes to the Translation of Hoffineister's Papers in 

 the Annals of Nat. Hist., 3d ser. I. p. 7. 



