HALF-AN-HOtJR AT THE MICROSCOPE. 43 



which it does not stain is not known, but that it has some, is 

 evident, from the difference of the action of aniline dyes to those 

 specimens prepared with gold. For example, take the tail of a 

 young rat or mouse, place in J % solution of gold chloride for an 

 hour or two, then decalcify and harden as usual. Very thin 

 sections should be cut and stained, first in rosanilin and then in 

 iodine green. It will be found that the periphery shows gold 

 staining, bringing out the tendon cells and giving a dark hue to 

 everything for a certain distance from the outside ; but within, a 

 great variety of colour will be found. In the middle the bone 

 trabeculae will be seen faintly stained, the calcified cartilage in 

 their centre is stained a bright colour, totally different from the 

 rest. All these colours may be varied by using different anifine 

 colours ; a pretty result may be obtained by simply staining with 

 iodine or methyl green. 



1balf=*an=*1bour at tbe flDicroecope 



mttb /IDr. Uutfen mest, 3f,XS., ff.lR./ID.S,, etc 



Seeds of Campanula earpatica (PI. V., Fig. i). — Seeds have 

 been much less frequent visitants in our travelling boxes than 

 they deserve to be, both on account of their beauty and interest. 

 Would the exhibitor of the present slide enlighten us as to the 

 cause of the iridescence here shown ? It would be necessary to 

 make transverse sections, and then to separate each coat of the 

 testa, mounting each in glycerine jelly. It will probably be found 

 that the external walls of the cells forming the outer seed-coat are 

 exceedingly thin, and in consequence polarise the light passed 

 through them ; a similar property being possessed by superimposed 

 plates of glass, as is familiarly known to soiree attenders. In 

 some cases the membrane named is so thin that it is difficult to 

 believe it present when the seed is viewed as an opaque object ; 

 this may be well seen in the seed of the ^^'hortle-berry ( Vaccitiium 

 myrtillus). In the seeds of a very extensive natural order, the 

 Sola7iacece^ the outer membrane becomes entirely absorbed during 

 the process of ripening, whence arise appearances very difficult of 

 explanation, without watching the changes during development. 



