OF THE GREEN CELLS OF PLANTS 65 



crystals are colourless, and the wash-water is only pale yellow 

 without any trace of red. The solution is then made up to 50 c.c. 

 and kept in a Jena glass flask, for the alkali which is slowly dissolved 

 out from ordinary glass rapidly turns the solution pink. The 

 reagent should be pale yellow when used, in order to obtain the best 

 effects, and does not keep in. good condition for more than a few 

 days. 



After the chlorophyll and fats have been removed from the tissue 

 by allowing it to stand in cold alcohol, or by boiling up with alcohol, 

 the colourless tissue must be well washed with water, and the water 

 used must, as described above, be doubly distilled from glass. 



The staining process may be watched in progress, when it will 

 be found that escaped chloroplasts from ruptured cells take on 

 the stain first, and in many cases show a deep purple-blue within 

 a few minutes. Within the intact cell the stain does not pene- 

 trate so rapidly, and the cell wall may show a blue staining in 

 some cases before the contained chloroplasts, but eventually these 

 also stain a deep blue, sometimes preceded by a dark brown. The 

 nuclei of the green plant cells also stain a deep blue (unlike animal 

 cell nuclei), and there is usually a much slighter diffuse blue in the 

 remaining cytoplasm. The fibres associated with the vascular 

 bundles also show in many cases a blue staining. This probably 

 means that the iron salts are carried along this route to the green 

 cells. But the early and deep staining of chloroplasts and nuclei 

 is characteristic in the preparations. 



In addition to tissues containing chloroplasts, several prepara- 

 tions have been made from plants not containing chlorophyll, such 

 as yeast, moulds, and larger fungi. There is a marked contrast 

 found here : a blue stain does not appear for some days, and then in 

 only a comparatively feeble manner. The conidia and the conidio- 

 phores show more iron than the mycelium filaments. It is probable 

 that this slow and feeble staining is due to organic iron compounds 

 slowly breaking up and yielding traces of inorganic iron. 



A series of ash analyses of chlorophyll- containing and chlorophyll- 

 free plants show in all cases a much higher percentage of iron in the 

 ash of the green plant ; this furnishes presumptive evidence that 

 iron plays an important part in photo- synthesis. 



A large number of plants of different types have been examined, 

 and the main results are given in the following account. 



Amongst unicellular green plants there were examined chlorella, 



5 



