328 President' a Adchrss. 



the influence of light to have lost its power of swelling in water 

 and watery solutions, and in this, as in the retention of its form and 

 shape, we have a marked difference between the destructive effects 

 of light and of heat. 



The different elements and constituents of the chlorophyll- 

 corpuscles behave difierently when exposed to intense light. Some 

 are affected, others are not, and it is the merit of this method of 

 investigation that it enables a direct study to be made of the 

 relations of these constituents to respiration. 



Starch and oil have, from their easy recognition, been often 

 hitherto regarded as the only products of the function of the 

 chorophyll-corpuscles. In some cases, when neither starch nor oil 

 has been found, and abundance of glucose or mannite has been 

 discovered in the leaves of a plant, these substances have been 

 considered as the product of the chlorophyll-corpuscles. But neither 

 starch, oil, nor sugar are the only products, nor, indeed, the only 

 visible ones. Pringsheim in one case observed highly oxidised 

 bodies of the group of organic acids directly formed in the chloro- 

 phyll-corpuscles, and this makes it probable that of the bodies 

 hitherto considered to be fat or oil-drops may consist of substances 

 of a very different character. Again, in Mesocarpus scalaris, at all 

 stages of development and in every cell, there may be seen numerous 

 (almost covering the chlorophyll-plate) small, oil-like, glistening 

 globules of different sizes, and very like the small oil globules in the 

 bands of Spirogyra, which, as they disappear on the addition of 

 alcohol and ether, might at first be regarded as fat or oil globules. 

 They are clearly formed in and secreted by the chlorophyll-plate, 

 and pass out from it into the protoplasm of the cell. These are not 

 oil globules, but vesicles with a. resisting pellicle, enclosing a content 

 in greater or less part consisting of tannin. They may be termed 

 tanuin vesicles. The dark coloration and coloured precipitate 

 formed with iron salts, potassium bichromate, and with ]\Iillon's 

 reagent, conclusively indicate their nature. The form of these 

 vesicles is easily destroyed by slight warmth, mechanical irritation, 

 or any decomposition which will end in the death of the cell, and 

 when destroyed the contents disappear, mixing with the cell sap, 

 and the pellicle is then indistinctly seen appressed to the chlorophyU- 

 plate, and giving its surface a netted or froth-like aspect. 



In addition to all these substances the oily vehicle of the 

 chlorophyll colouring matter and the hypochlorin must be reckoned 

 as contained elements of the chlorophyll-corpuscles and as normal 

 products of their function. 



Of the constituents just mentioned, those which are rich in 

 oxygen and occur as grains, globules, or vesicles, — the starch grains, 



