FORMATION OF CELLS— TISSUES 



311 



and possibly in Achlya (fig. 667), or may remain always in 

 the cell in which they are developed, as is generally the case with 

 oospheres. When the fusion takes place, protoplasm unites with 

 protoplasm, nucleus with nucleus, &c., and a new cell results 

 which clothes itself with a cell-wall, and becomes a new indivi- 

 dual. The process of fusion of dissimilar cells is generally 

 called fertilisation; that of union of similar cells is known as 

 conjugation. The new cell formed by the fusion is a zygote ; 

 in the first case it is sometimes called an oospore, in the second, 

 a zygospore. 



Fig. 668. 



Fig. 668. Small-ceUed meristetn at apex of root of Phanerogam. 



The Tissues. 



By one or other of the vegetative methods of cell-production 

 described, the original unicellular plant becomes a multicellular 

 body, and its ultimate form may be that of a row of cells form- 

 ing a filament, or a flat plate, one or a few cells thick, or, again, 

 a mass of cells of very variable size and shape. We have seen 

 that in such a mass different cells or aggregations of cells are 

 specially set apart to discharge particular duties. Such collec- 

 tions of cells are called tissues. Thus we speak of the tissues of 



