GENERATION OF UNICELLULAR PLANTS. 245 



Plants exactly resemble that from which they sprang ; whilst in 

 the case of more highly organized Plants, they gradually become 

 differentiated to a greater or less degree, so that special ' organs ' 

 are evolved, which take upon themselves dissimilar yet mutually 

 dependent actions in the economy of the entire Organism (§ 181). 



186. The process which represents the Generation of the higher 

 Plants is here performed in a manner so simple that it would not be 

 recognized as such, if we were not able to trace it up through a 

 succession of modes of gradually increasing complexity, until we 

 arrive at the elaborate operations which are concerned in the pro- 

 duction and fertilization of the Seeds of Flowering Plants. For it 

 consists in nothing else than the re-union or fusion-together of any 

 pair of Cells (Plate vm. Fig. 1, k), — a process which is termed Con- 

 jugation ; and it is characteristic of this humble Plant, and shows 

 how imperfect must be the consistence of its Cell-membrane, that 

 this seems to enter into the fusion no less completely than do the 

 Cell-contents. The communication is at first usually made by a 

 narrow neck or bridge (k) ; but before long it extends through a 

 large part of the contiguous boundaries (l) ; and at last the two 

 cells are seen to be completely fused into one mass (m), which is 

 termed the Spore. Each Spore thus formed is the Primordial Cell 

 of a new generation, into which it evolves itself by successive re- 

 petitions of the process of binary subdivision. — It is curious to 

 observe that during this Conjugating process a production of Oil 

 particles takes place in the cells ; these at first are small and 

 distant, but gradually become larger and approximate more closely 

 to each other, and at last coalesce so as to form oil-drops of various 

 sizes, the green granular matter disappearing ; and the colour of 

 the conjugated body changes, with the advance of this process, 

 from green to a light yellowish-brown. When the Spore begins to 

 vegetate, on the other hand, producing a pair of new cells by binary 

 subdivision, a converse change occurs ; the oil-globules disappear, 

 and green granular matter takes their place. Now this is precisely 

 what happens in the formation of seed among the higher Plants ; 

 for Starchy substances are transformed into Oil, which is stored up 

 in the Seed for the nutrition of the embryo, and is applied during 

 Germination to the purposes which are at other times answered by 

 starch or chlorophyll. — The growth of this little plant appears to 

 be favoured by cold and damp ; its generation, on the other hand, 

 is promoted by heat and dryness ; and it is obvious that the Spore - 

 cell must be endowed with a greater power of resisting this than 

 the vegetating plant has, since the species would otherwise be 

 destroyed by every drought. 



187. If the preceding sketch really comprehends the whole Life 

 history of the humble plant to which it relates, this history is 

 much more simple than that of other forms of Vegetation, which, 

 without appearing to possess an essentially-higher structure, pre- 

 sent themselves under a much greater variety of forms and condi- 



