President's Address. 311 



the action of steam or treating them with dilute acids. Different 

 effects are produced according as one or other, or a combination of 

 these agencies, is made use of; but they coincide in this general 

 effect, that they cause the colouring matter, along with certain fluid 

 or semifluid substances accomi)anying it, to exude from the chloro- 

 Ijhyll-corpuscles in the form of larger or smaller drops, while these 

 coat the periphery of the decolorised skeleton or ground-substance 

 which, itself retains the original form of the corpuscle. 



If a portion of green tissue be warmed for fifteen minutes to an 

 hour in water of a temperature of 50° to 80° C, or if it be 

 suspended during fifteen minutes to several hours in a flask, so 

 as to be in contact with the steam of boiling water (the degree of 

 temperature and the time required for the action varies with the 

 tissue taken ; in most cases boiling the tissue for five minutes is 

 the quickest and most convenient procedure), viscid drops of vary. 

 ing size become visible at the circumference of the clilorophyll- 

 corpuscles. They may be watched exuding from the substance of 

 the corpuscle, in number depending upon the duration of the 

 operation. Always coloured, they are usually chlorophyll-green, 

 but this may be brighter or darker, and the tint in some cases is 

 yellow or blue-green, occasionally olive-green, more seldom reddish- 

 brown. They are completely soluble in alcohol and ether, and 

 consist of the colouring matter with an oily basis, which is the 

 vehicle holding it and the substances accompanying it in solu- 

 tion. 



In pioportion as the exudation proceeds, the ground-substance is 

 decolorised, and the colouring matter may be completely removed 

 from it. The structure of the ground-substance then becomes 

 visible, and it appears under a high magnifying power as a 

 skeleton, having the shape of the original chlorophyll-corpuscles, 

 composed of a soft substance differentiated to form a hollow 

 body, the circumference of which is abundantly pierced in 

 a sieve-Hke manner. It has, in fact, the character of a hollow 

 sponge. It is difficult to accomplish complete decolorisation by 

 heating in warm water alone, and this is best and most easily 

 brought about by a combination of warmth and dilute acids. The 

 character of the tissue must be taken into account, as for difterent 

 tissues one or other method may be more favourable. This 

 character of the ground-substance becomes evident if the corpuscle 

 be decolorised by alcohol or other solvent, and also, as wiU be 

 presently described, by the action of intense light ; and the fact 

 that the operation of these difterent agencies demonstrates the same 

 structural characters in the decolorised chlorophyll-corpuscles is 

 strong evidence that this is also the structure of the corpuscle 



TRANS. BOT. SOC. VOL. XIV, Y 



