DR, EDWARD SCHUNCK ON INDIGO-BLUE. 231 



produce, wlieii seen in the mass, a uniform blue coloration, 

 more or less intense. The darker colour of some leaves is 

 simply the effect of a greater crowding of the blue particles 

 in each individual cell, the cells of the paler leaves con- 

 taining fewer of these little masses, sometimes hardly any. 



Mr. Charles Bailey, to whom I gave some specimens of 

 leaves of Polygonum tinctorium coloured blue, had the 

 kindness, at my request, to submit them to microscopic ex- 

 amination, and gave the following as his opinion thereon : — 



'^The colouring-matter left in these specimens would 

 seem to be what Nageli terms ' crystalloids / and, with 

 one exception, these bodies are, as far as my examination 

 has gone, confined to the interior of the cells of the paren- 

 chyma. I do not see the least trace of any of this colour- 

 ing-matter occurring in the intercellular spaces. The only 

 part of the tissue where I find it, other than the parenchyma, 

 is in the cells of the stomata ; but it occurs nowhere else in 

 the cuticle." 



Bletia Tankervillice. 



The occurrence of a blue colouring-matter in this and 

 other plants belonging to the Orchidacese, such as Calanthe 

 veratrifolia, was first noticed by Clamor-Marquart * and 

 by the late Dr. Grace Calvert f. The attention of these 

 observers was directed to these plants by seeing a blue 

 coloration appearing in the white petals of the flowers 

 on their beginning to fade ; and they found the blue 

 colour to be due to indigo. In accordance with the views 

 then prevailing, they assumed the preexistence of the 

 colouring-matter, either as indigo-blue or as its hydride, in 

 the tissues of these plants. It is easy to see, however, on 

 reading the accounts of their experiments, that the 

 colouring-matter was really formed during the processes 



* Buchner, Repertoriuiu f. die Pharmacie, B. Ivii S. i. 

 + Journal de Pharmacie, t. vi. p. 15^. 



