304 President' a Address. 



for the past century attracted the attention of botanists 

 and chemists, and now the zoologist also found that it fell 

 within his domain. Although a vast amount of literature 

 on the subject existed, yet we were still far from having 

 an accurate knowledge of its character, of its origin, and 

 of the part it plays in the plant economy, Recently a 

 systematic investigation from an, entirely new standpoint 

 by Pringsheim had resulted in the elaboration of a new 

 hypothesis, which had been termed the " screen hypothesis" 

 of the function of chlorophyll and of its use to plants, and 

 he (the President) proposed to give to the members of the 

 Society a brief account of Pringsheim's work and hypo- 

 thesis. 



In the first place, however, he gave an historical resume 

 of the subject, and explained the views current regarding it 

 up to the present time. He pointed out, as regards tlie 

 occurrence of chlorophyll in plants, that with few excep- 

 tions it is found in parts to which light has access, and that 

 in the simpler plants the green colour is often diffused through 

 the whole protoplasm of the plants, but in highly differen- 

 tiated forms it is usually relegated to isolated portions of 

 the protoplasm, which constitute chlorophyll-corpuscles. 

 Since Pelletier and Caventon gave the name chlorophyll 

 to the green colouring matter of plants some confusion has 

 attended its application. By some authors the term has 

 been used as including both the green colouring matter 

 itself as well as the protoplasm skeleton in which it is 

 incorporated, by others to designate the former of these 

 only, whilst recently Wiesner has retained it for a portion 

 only of the actual colouring matter. Bohm introduced 

 the term ''chlorophor" for the protoplasmic groundwork, and 

 the cumbrous expression "materia viridis" for the impreg- 

 nating green matter, but these have not come into general 

 use. Writers now speak of the skeleton as the body or 

 corpuscle, which may be coloured or colourless, otherwise 

 true or false, — (Sachs first showed, and after him the subject 

 has been worked out by Dehnecke and Schimper, that the 

 corpuscles may exist without the green colouring matter, 

 and tliese he designated leucophyll or false, as contrasted 

 with those which are green, tlie true or chlorophyll), — 

 of the chlorophyll colouring matter or chlorophyll, and 



