692 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



or midrib. It is a curious circumstance that when a plant which 

 exhibits the cyclosis is kept in a cold dark place for one or two 

 days, not only is the movement suspended, but the moving particles 

 collect together in little heaps, which are broken up again by the 

 separate motion of their particles when the stimulus of light ami 

 warmth occasions a renewal of the activity. It is well to collect the 

 A (> specimens about midday, that 



being the time when the rotation 

 is most active, and the move- 

 ment is usually quickened In- 

 artificial warmth, which, indeed, 

 is a necessary condition in some 

 instances to its being seen at all. 

 The most convenient method of 

 applying this warmth, while the 

 object is on the stage of the 

 microscope, is to blow a stream 

 of air upon the thin glass cover 



through a glass or metal tube 

 FIG. 529. Tissue of the testa or seed-coat 



of star-anise : A, as seen in section ; 

 B, as seen on the surface. 



in 



spirit- 



previously -heated 



lamp. 



The walls of the cells of 



plants are frequently thickened by deposits, which are first formed 

 on the inner surface, and which may present very different appear- 

 ances according to the manner in which they are arranged. In 



FIG. 530. Section of cherry-stone, 

 cutting the cells transversely. 



FIG. 531. Section of coquilla 

 nut, in the direction of the 

 long diameter of the cells. 



its simplest condition such a deposit forms a thin uniform layer 

 over the whole internal surface of the cellulose wall, scarcely detract- 

 ing at all from its transparency, and chiefly distinguishable by the 

 * dotted ' appearance which the membrane then presents (fig. ~)-2Z. A). 

 These dots, however, are not pores, as their aspect might naturally 

 .suggest, but are merely points at which the deposit is wanting, so 



