THE MOLECULAR FORCES IN PLANTS. 119 



a higher temperature, e.g. 30 C., for about three hours, at a lower 

 for a longer time), and then examine microscopically. The proto- 

 plasm of the cells, owing to reduction of the Silver salt in the 

 solution, has stained black ; but it is specially important to observe 

 that this reaction only takes place when the cells were living at 

 the commencement of the experiment. Spirogyra cells killed by 

 heat, or alcohol, or otherwise, only acquire a yellow or brown 

 colour on exposure to the alkaline Silver solution. The protoplasm 

 of originally living cells of Spirogyra blackens somewhat more 

 slowly, but even better, if we lay a few filaments of the alga in 

 a solution composed of 10 mg. of Silver nitrate and 5 c.c. of lime 

 water, to 1 litre of water. In this case, access of air containing 

 Carbon dioxide is to be carefully avoided during the reaction. 



According to my view, the blackening of the protoplasm of cells 

 brought into contact, while living, with the Silver solutions, is at 

 least frequently due essentially to the reduction of the Silver salt 

 by non-nitrogenous bodies, of the nature of aldehydes, which, 

 together with amido-acids and acid amides, are produced in the 

 decomposition of the living proteid molecules. Dead proteid 

 molecules have no such effect on the Silver solution, since they 

 do not decompose like the living proteid molecules. 



We now pass on to the cell-nucleus. That this contains proteid 

 substances is shown by its behaviour towards reagents. In con- 

 tact with iodised Potassium iodide solution (prepared by dissolving 

 G'050 grm. of Iodine and 0'200 grm. of Potassium iodide in 15 c.c. 

 of distilled water), the cell-nucleus takes on a yellowish colour. 

 Methyl green Acetic acid (prepared by adding methyl green to 

 1 per cent. Acetic acid) stains the nucleus very beautifully. On 

 treating the cells with these reagents the nuclei stand out more 

 conspicuously, which is often a matter of considerable importance. 

 The nuclei of the epidermal cells of Aspidistra leaves stain very 

 beautifully with methyl green Acetic acid, as I have often found. 

 To familiarise ourselves with the reaction of nuclei towards iodised 

 Potassium iodide solution, we investigate the epidermal cells of 

 the leaf of Escheveria globosa, or delicate transverse sections 

 through the first leaf sheath of young maize seedlings. In the 

 cells of the parenchyma of the sheath are present fairly large cell- 

 nuclei. Beautifully developed nuclei are present in the cells 

 adjoining the stomata on the under side of the leaf of Tradescantia 

 virginica. We can easily ascertain that this is the case by micro- 

 scopic examination of strips of epidermis from the leaves. 



