42 PRACTICAL BOTANY 



object. Various kinds of selenite-plates may be used : it is 

 assumed here that the plate shows red and green tints. Mount 

 a section of a twig or of a leaf-stalk ; rotate the analyzer 

 so that the field is red or green. The interference colours 

 will not be well seen in the thin cell- walls ; they will appear 

 merely red or green. The thickened cell- walls will exhibit 

 a play of colours which differs in different cases. 



Mount a section of part of a succulent leaf (Aloe, Crassula, 

 Sedum, &c.). Observe that the interference colours in the cuticu- 

 larized external layer of the outer walls of the epidermal cells are 

 complementary in position to those of the subjacent cellulose 

 layers ; this indicates differences of tension in the cuticularized 

 and uncuticularized layers. 



II. Protoplasm and Nucleus. 



The protoplasm of the cell, and the nucleus, may be 

 observed in the living condition as described in the pre- 

 ceding chapter ; but in order to recognize the more 

 minute details, and in order to make permanent pre- 

 parations of these bodies, more complicated methods of 

 treatment are necessary. 



The protoplasm and nucleus must first be fixed and 

 hardened (see above, p. 4) : the best hardening agent 

 is absolute alcohol; if picric acid be used it must be 

 very completely washed out from the tissues before 

 staining. 



Harden the young flowering stem of a common 

 Hyacinth, not more than three or four inches in length, 

 in alcohol. : cut longitudinal sections of the basal portion 

 of it, and stain with Kleinenberg's hsematoxylin (see 

 Appendix A) till the sections are deeply coloured, then 

 wash thoroughly with absolute alcohol in a watch-glass : 

 transfer them (drying off all superfluous alcohol with 

 blotting paper) to oil of cloves, or turpentine and creo- 



