The roses shown on the accompanying figure are white with a delicate and beautiful network of blue veins. Such roses can be obtained in little more than one hour by placing the following solution, instead of water, in the vase in which the cut ends of the stalks are dipping:

Fig. 186 - The roses are covered with a network of blue veins.

Water....................... 100 cubic centimeters.

Aniline methylene blue........ 2 grammes.

Potassium nitrate ............ 2 grammes.

School boys know that white roses can be transformed into red flowers by allowing the cut end to remain some time in some kinds of red ink. The writer tried to obtain similar results with a number of aniline dyes and found that while some, like aniline red scarlet, for cotton, readily rise into the vessels of the stalk, others, like aniline methyl green, will not, under any circumstances reach the flowers. Some common salts were added to the dyes and one of them, potassium nitrate (saltpeter) was found to exert a powerful influence over the ascent of the dyes, which rise then rapidly and in considerable quantities. The experiment is curious and should be repeated while using the blue liquid: the end of a few stalks being placed in some of the solution to which no saltpeter is added. Aniline methylene blue is not one of the dyes which readily ascend in plants and it will be soon noticed that, while the flowers with the stalks dipping into the saltpeter and blue dye solution are covered with the blue network, nothing can yet be detected on those whose stalks are allowed to dip in the same liquid but without saltpeter.

Will some botanist suggest an explanation of this influence of saltpeter on the ascent of dyes in stalks and flowers?