NOTES AND MEMORANDA. 309 



in distributing the spores in large vessels, and tlie effect of light on 

 the movements of other plant-organs. 



The following are the general results arrived at : — 



The direction of the movement of certain swarnispores is influenced 

 by the light : these may be termed phototactic. This action is con- 

 nected only with the protoplasm as such, and not with any definite 

 colouring matter, for colourless spores act like coloured ones. 



The swarmspores affected by light move in the direction of the 

 incidence of the light, and this takes place in two ways : either it is 

 constant only in the direction of the source of light even when the 

 intensity of the light decreases in this direction, when the swarmspores 

 may be called aphotometric ; or they follow the decrease of light in 

 the direction of rising or falling intensity, when they may be called 

 photometric. No movement is possible in any other direction than 

 that of the incidence of the light, even when the intensity of the 

 illumination rises or falls in any other direction. 



The blue, indigo, and violet rays alone have any influence on the 

 phototactic spores, and the maximum effect is produced by the indigo. 

 On the other hand, the yellow and nearly allied rays of sufficient 

 intensity cause a quivering movement in phototactic spores. 



On a sudden change in the brightness, many phototactic swarm- 

 spores show after effects, the direction of the movement induced by the 

 previous degree of brightness being retained for a short time. 



The large swarmspores of Bryopsis show after effects only when the 

 intensity of the light is suddenly diminished ; when it is suddenly 

 increased, they exliibit a trembling which makes them leave their 

 course for a while. Those of JBotrydium do not show after effects 

 when the brightness is either suddenly increased or decreased, but 

 they tremble if the light is suddenly cut off. The swarmspores of 

 TJlvcB gave no sign either of after effect or trembling. 



An increase in the intensity of the light occasions in the photo- 

 tactic spores for the most part a tendency to settle ; direct sunlight 

 more particularly acts in this way ; decrease in the intensity of the 

 light heightens their mobility. 



The rapidity of the movement is not influenced by light ; the 

 spores, however, move in a more direct course the greater the intensity 

 of the light. 



In general, moreover, the smaller spores move straighter than the 

 larger ones. The largest, by vii'tue of their important property of 

 moving in considerable masses, have freed themselves from the 

 influence of light on their direction. But there are also small spores 

 which are influenced comparatively slightly, or not at all, by light. 



In the dark the phototactic swarmspores do not settle to rest 

 unless they are sexually differentiated and unite with one another. 

 Otherwise they continue to move till they disappear. 



In swarmspores brought from the dark into the light, similar 

 effects may be observed as when subjected to a sudden increase in the 

 brightness. 



In general, photometric swarmspores alter in their sensitiveness to 

 light in the course of their development, this being displayed more 



