312 President's Address. 



under normal conditions. Chlorophyll-bands, plates, and masses 

 show equally well this structure. 



These, the normal effects of heating a tissue in water or exposing 

 it to steam, may be complicated by the temperature being so high 

 as to affect the starch contained in the chlorophyll-corpuscles, and 

 by causing the granules to swell and rupture the corpuscle, thus 

 destroy its form. All tissues are not equally sensitive in this way. 

 Some may be subjected for hours to the action of water at a high 

 temperature, or to steam, without the chlorophyll-corpuscles losing 

 their structural character, whilst in others a few minutes suffices to 

 cause them to lose their form and to coalesce ; or, and perhaps 

 more usually^ whilst retaining their individuality, they swell 

 internally and rupture, and then ajjpear as irregularly burst hollow 

 spheres. The amount of starch present in the chlorophyll-corpuscles 

 determines to a certain extent the rapidity of this effect. The more 

 starch present the more certainly and the more easily will it be 

 produced ; but there are many tissues in which starch is present, 

 and yet there is complete immunity from this action. This 

 rupturing of the chlorophyll-corpuscles, due to the starch, must 

 be distinguished from the exudation of colouring matter and its 

 accompanying substances already mentioned, which is quite inde- 

 pendent of the starch content, and is brought about at a much 

 lower temperature. 



The exudation of the coloured drops appears to be the mechanical 

 effect of a simple swelling of the ground-substance due to its 

 absorbing water, and it thereby exercises a pressure upon and 

 squeezes out the vehicle holding the colouring and other matters 

 in solution which fills its meshes. 



The effect of treating green tissues with dilute acids is somewhat 

 different, and has led to the discovery of a universally present 

 constituent of the chlorophyll-corpuscles, — hypochloriu. Hydro- 

 chloric acid, in the proportion of 1 vol. to 4 vols, of water, is the 

 most favourable for the detection of this substance. But others 

 may be used, e.(j., sulphuric acid, 1 vol. to 20-40 vols, of water ; 

 glacial acetic acid, 1 vol. to 2-4 vols, of water ; picric acid, 1 vol. 

 to 3-6 vols, of water; these, however, require much care in appli- 

 cation, and are less certain in their effect than hydrochloric acid, 

 which has been chiefly used in these investigations. Glacial acetic 

 acid, 1 vol. to 2 vols, of water, is specially favourable for bringing 

 out the perforated wall structure of the chlorophyll-corpuscles. 



In specimens preserved for some years in Hantz's fluid, in dilute 

 glycerine, and in chloride of calcium, hypochloriu was observed to 

 have exuded from some chlorophyll-corpuscles. 



If a green tissue be treated with dilute hydrochloric acid, a sudden 



