308 



MANUAL OP BOTANY 



dons. The original nucleus of the mother-cell of the spores ilivides 

 into two as described above. The spindles disappear, and each 

 nucleus divides again. New spindles are next formed between 

 the four nuclei (fig. 664, b), and then cell-plates or cell-walls 

 are simultaneously developed between them, giving rise to 

 four so-called special moth'er-cells, each of which develops a 

 spore. The division of the protoplasm in this case is often 

 preceded by a thickening of the cell-wall at the places to 

 which the new septa will be attached, so that the protoplasm 

 is partially separated before the new walls appear. 



In ordinary cell- 

 FiG. 66-I-. division the two cells 



are usually of the 

 same size- In some 

 cases a variation in 

 this I'espect is seen, 

 as in the cells of the 

 Yeast plant. These 

 often put out a late- 

 ral protuberance of 

 smaller size, which is 

 gradually abstricted 

 off by the formation 

 of a cell- wall. _ This 

 .variation _ is known 

 It is not uncommon 



Ficf. 664. Hellehorus ftelidux. A-fter Strasburger. 

 ( X 540.) Quadripartition of mother-cell of pollen : 

 in B the connecting threads and cell-plates are 

 shown; in A the walls have been formed. Only 

 three are visible, the fourth not 'being in focus ; 

 the mode of development is tetrahedral. 



as buddinff, or gp.mination (fiy. 662) 

 among the lower Thallophytes. 



In a few cases in some of the lower plants the division of the 

 cell is not preceded by division of the nucleus. In others, after 

 the nucleus has divided, the new cell-wall is formed by an 

 ingrowth from the walls of the original cell. 



Free Cell-formation. — In this method of cell formation the 

 nucleus divides repeatedly ti]l a number of nuclei are formed. 



The protoplasm aggregates round each nucleus, and a 

 number of naked cells are so formed in the interior of the 

 original cell. In some cases, as in the formation of the zoo- 

 gonidia and gametes of many Algse and Fungi (fig. 665), they 

 remain naked and are discharged in this condition from the 

 cell in which they are formed. In other cases, each new cell 

 secretes a cell-wall round itself. 



In its simplest form, this mode of cell-production results in 

 the formation of a number of isolated cells (fig. 665). In certain 

 cases, however, the cells are combined into a tissue, as in the 



