60 IV. PLASTIDS. 



grains on one leucoplast occur not infrequently. After further 

 growth such grains presently come into mutual contact, and 

 may receive thenceforth layers which are common to the 

 two. These and similar phenomena lead, here and in other 

 cases, to the formation of compound or semi-compound starch 

 grains. 



Starch Formers in Pellionia. A plant which has starch formers 

 quite similar to those of Iris, but much more easy to see, is the 

 pretty Urticaceous hot-house creeper, Pellionia Daveauana. The 

 plant can be very readily cultivated, and multiplies and spreads 

 freely. The starch formers can be found in every cross-section 

 taken through quite young parts of the stem. They are here 

 green, and therefore in this respect are not true leucoplasts, but 

 in their function are so far related to leucoplasts that they 

 form the greater portion of their starch, not through their own 

 assimilation, but from migrated reserve food-materials. The 

 circumstance that they are green makes them readily visible ; 

 a slime with which the section becomes covered protects them 

 from the injurious action of the water. Here also the starch 

 grains which are produced by the starch formers become very 

 large, and show a strongly eccentric structure. At the end of 

 the starch grain most remote from the organic centre, the starch 

 former is still to be seen as a green cap. 



Fixing and Staining Chromatophores. It is usually somewhat 

 difficult to "fix " chromatophores in an unaltered condition. The 

 best medium for this purpose is a saturated solution of picric acid 

 and corrosive sublimate in alcohol. The action of this must be 

 continued for about twenty-four hours, and the material then well 

 washed in running water. Treated in this way the material does 

 not usually show the formation of disturbing needle-shaped or 

 sphere-crystals of corrosive sublimate ; but if the washing is im- 

 perfect they may be subsequently removed by running through 

 alcoholic solution of iodine of a dark-brown colour. 1 In staining 

 the chromatophores acid fuchsin is recommended, made by dis- 

 solving 0-2 per cent, acid fuchsin in distilled water, and a little 

 camphor added to make the solution keep. The sections can lie 



1 Objects fixed in corrosive sublimate should not be touched with steel 

 forceps or section-lifters before washing, or globules of metallic mercury may 

 be produced. If forceps must be used they should have platinum or horn 

 tips. 



