MliRISTEM. 



43 



it is possible to detect here and there cells in -which typical division- 

 figures (mitosis) can be made out, especially where a thin section is 

 cut and stained as directed in the note at the end of Chapter ii. 

 (see Fig. 28). In these young cells the cell-walls are very thin, 

 and on account of turgiditj- are a good deal on the stretch ; the 

 polyhedral shape so often observed in the cells of young tissues 

 is due partly to mutual cohesion and pressure; and, moreover, a 

 certain amount of intercellTilar matrix (which forms the middle- 

 lamella) is soon secreted which tends to make the cells cohere. 

 If the intercellular substance is dissolved by certain reagents,' 

 the cells may be made to separate from one another, and 



Fig. 28. — Youj<G Dividing Cells fkoji a Ruuimknt.\uv Tissuk. 

 one cell the nucleus is undergoing division (mitosis). 



-In 



they then tend to resume the spheroidal shape. The direc- 

 tions in which fresh cell-walls are formed is determined to a 

 certain extent by the directive action of the protoplasm, and 

 by the relative position of the cells in the young tissue. In 

 buds or root-tijjs it is possible to make out two main modes 

 of wall-formation with regard to their direction in .space, and 

 these are known by the terms synclinal and anticlinal. The 

 synclinal walls are formed more or less parallel to the external 

 contour of the bud, or the contour of the central cylinder, whilst 

 anticlinal walls are those formed at right angles to these. The 



* Schulze's Macerating Mixture (see infra). 



