66 IKON COMPOUNDS IN THE CHLOKOPLASTS 



obtained as plankton from a green- coloured pond- water; pleuro- 

 coccus, obtained in nearly pure condition growing on an oak 

 fence near Oxford, and stained and examined in collaboration with 

 Mr. Edward Whitley ; several forms of diatom and several unicellular 

 forms found in lichens. 



The blue-black effect is very readily obtained with these uni- 

 cellular green plants, often without previous removal of the chloro- 

 phyll. In the case of the lichens the contrast is marked between 

 the green cells and the fresh hyphse of the fungus, but dead or 

 decaying fungal matter often gives a blue stain. 



The algae observed were species of vaucheria, spirogyra, ulva, 

 and ulothrix. The effects were often repeated in several experi- 

 ments, both with hsematoxylin staining and with ferricyanide and 

 hydrochloric acid. The ferricyanide solution does not appear to 

 penetrate well, and only some filaments in an alga like spirogyra 

 are coloured, but the staining has been obtained within an hour or 

 two of treatment with this reagent, and is a very beautiful effect 

 when obtained in spirogyra. The light blue colour follows the 

 spirals of the chlorophyll bands, and the granules are obviously more 

 deeply blue than the rest of the bands. The deep blue-black with 

 hsematoxylin is more readily and uniformly obtained, coming often 

 within a few minutes of applying the stain to the decolorised alga, 

 and furnishing again a beautiful effect. Sometimes, however, the 

 brown colour of colloidal iron is obtained in spirogyra. 



Ulva latissima gives a very deep blue-black coloration, rendering 

 the cells almost opaque ; its ash shows a high content in iron. 



Cladothrix, when growing in water containing small amounts of 

 iron, as is well known, secretes, or excretes, a tube of iron oxide 

 around the filaments, and is then known as an " iron bacterium." 

 When these so- called" iron bacteria " are treated with hamiatoxylin 

 they turn blue- black almost instantly, and if the stained specimens 

 are examined under the microscope the interesting fact is im- 

 mediately observable that not only the external tube, but the sub- 

 stance of the organism itself, is stained blue- black, so settling a much 

 disputed point. The same is seen in vaucheria an incrustation of 

 iron- oxide particles is demonstrable in the gelatinous sheath sur- 

 rounding the filaments, either by ferricyanide or hsematoxylin 

 staining, but, in addition, both reagents show inorganic iron within 

 the filament itself. 



Many higher aquatic plants, such as lemna and elodea, possess 



