President's Address. 331 



and may be found with embedded skeletons of clilorophyll-corpuscles 

 still lining the cell wall months after insolation. The reason for 

 this is a partial destruction of the protoplasm, which is the imme- 

 diate effect of the light, and as light only acts in presence of oxygen 

 it is clear that the oxygen must combine with certain elements of 

 the protoplasm of the utricle, and, as a result of the combustion, 

 that change and diminution of its substance occurs which produces 

 a loss of contractility. 



The loss of substance by oxidation in light may at times be made 

 directly visible. If a filament of Spirogyra (one-spired species are 

 more suitable, as in them the utricle is not strongly developed), some 

 cells of which have been insolated, be treated with a reagent which 

 stains protoplasm deeply (iodine solutions, for example), a more or 

 less striking difference is observed between the contracted protoplasm 

 of the insolated and the non-insolated cells. In the non-insolated 

 cells the former lining protoplasm of the wall no longer forms a 

 continuous uniform layer or plasma-utricle, but is a contracted 

 Plasmodium net, in which are embedded, as in a matrix, small dense 

 granular or globular bodies. These, especially, are deeply stained 

 by the iodine. If the protoplasm lining the wall was originally 

 thick, they are numerous ; if it were thin, they are few in number, 

 sparingly distributed, and may be almost absent. But their number 

 depends on the species examined, as well as upon the thickness of 

 the utricle. In the insolated cells one can recognise with certainty 

 a diminution in the number of these small bodies. In them is 

 doubtless to be recognised the element that so readily takes up 

 oxygen under the influence of light, and by its combustion causes 

 the loss of substance in the protoplasm, whereon depends the 

 diminution in contracting power. It is often difficult to determine 

 the loss of protoplasm substance, and it can only be done by careful 

 comparison of insolated and non-insolated cells. 



Other striking changes after insolation in the protoplasm have 

 already been referred to as occurring in Spirogyra and in Nitdla. 

 In the former there is the displacement of the nucleus, vesicular 

 swelling of the centre plasma concurrently with a granular coagulation 

 of its substance and the occasional colouring of the same, and finally, 

 the rupture and knotting of the protoplasm threads. In the latter 

 there is the aggregation of the streaming protoplasm at the area of 

 insolation, &Q.. Many of these changes doubtless occur in general 

 death of protoplasm from other causes besides light, for example, 

 from heat or electricity, and it is therefore difficult, if not impossible, 

 to distinguish amongst them the specific action of light. 



Amongst the phenomena which fall to be noticed here is paralysis 

 of protoplasm, or temporary stoppage of its movement by light. 



