ON AVOAD AS A PKEHLSTORIC PIGMENT. 



37 



other leaves were brought home at the same time from the same place, 

 but they all passed into putrefaction without showing any trace of blue. 

 Professor Marshall Ward shortly after this drew my attention to a paper 

 which had just been published by Dr. Hans Molisch * in which he gives a 

 very simple method of demonstrating the presence of indigo in these 

 plants. It consists in simply keeping the fresh leaves in a closed vessel 

 filled with ammonia gas for twenty-four hours and then transferring them 

 for twenty-four hours into absolute alcohol. The ammonia causes the 

 indigo to turn blue, in which state it is insoluble in the alcohol, while the 

 last-named substance dissolves out the chlorophyl, so that when the 

 leaves are sectioned and mounted in balsam one can see not only that 

 indigo is present, but also the exact tissues in which it occurs, viz. in the 

 chlorophyl-bearing tissues, being absent from the cuticle, the hairs and 

 fibro-vascular bundles. Herr Molisch, in a letter to me, advised me to 

 examine by this method the very youngest leaves, such for instance as 

 were not more than an inch long. By doing this the presence of indigo 

 in the Parson Drove Woad was easily demonstrated, and it became equally 



Fig. 3. 



Woad Spud used at Parson Drove, and in the Fen-land generally, for weeding 

 Woad. This process is done by men and women kneeling. The handle is cut with 

 a crutch to fit the hand, and is generally made either of Willow or Hawthorn. The 

 spud figured was in use in a Woad field at Parson Drove in 1899 ; its cutting edge 

 showed signs of wear. 



apparent that the fully-grown leaves were late in the year practically 

 devoid of it. Such a leaf came out of the absolute alcohol a brittle, 

 yellowish- white object, while the growing leaves were distinctly blue. 



Marchlewski and Eadclifie t considered that indican consisted of 

 sugar and indoxyl, the latter being a very unstable substance (CSH7NO). 

 Professor Beijerinck j has recently controverted Breaudat's assertion of 

 the presence of an oxydase in Woad. He considers the indigo-producing 

 plants constitute two groups, one containing indican, such as Indigofcra 

 tinctoria, Polygonum tinctorum, &c., which yield a solution of indican 

 when treated with hot water, but if they be immersed in water below 

 50° C. and the air excluded will yield an indoxyl solution ; the presence of 

 an enzyme whose action is destroyed by the higher temperature being the 



* Molisch, H., " Ueber das Vorkommen von Indican in Chlorophyllkorn der 

 Indicanpflanzen," Bcrichte der Dentschen Botan. Gesell. 1899, Bd. xvii. Hf. 0, p. 2*28, 

 t. xviii. 



t Journal of the Society of Cheviical Industry, May 81, 1898. p. 480. 

 j Beijerinck, M. W., " On the Formation of Indigo from Woad," Koninklijkc 

 Akademie var\, Wetenschappen te Amsterdam, Oct. 25, 1899. 



