308 NOTES AND MEMORANDA. 



Strasburger first repeated most of the experiments of Sachs, both 

 with emulsions and with swarmspores, and found the same results in 

 every case. But besides these passive groupings of the swarmspores 

 caused by currents, he observed some that were caused by active 

 movements on their part. These were examined, not in large vessels, 

 but in drops which, hanging from the covering glass in a moist 

 chamber,* could be examined under the Microscope. 



The experiments were carried further by applying light of different 

 colours, either by passing it through different coloured solutions 

 before it reached the di*ops, or by directing the different parts of an 

 objective sj^ectrum on the drops. Lastly, in experimenting on the 

 action of heat, the incident rays were sometimes made to lose their 

 calorific rays by a concentrated solution of alum, sometimes their 

 luminous rays by a solution of iodine in bi-sulphuret of carbon. 



The very first experiment showed that in such drops certain swarm- 

 spores often moved in a direct course either to or from the source of 

 light ; that the movement often took place with considerable rapidity ; 

 that it commenced the moment the j)reparation was exposed to the 

 influence of the light ; that a change in the position of the prepara- 

 tion relatively to the source of light resulted in an immediate corre- 

 sponding change in the direction of the movement of the spores. It 

 had then to be determined whether any and what share in these move- 

 ments was so due to currents within the drop, and with this object the 

 same experiments were repeated with emulsion drops. The currents, 

 which could then be easily detected in the drop, were, however, under 

 the same conditions and in the same localities, not to one side only as 

 in the case of swarmspores, but always in a very different direction, 

 namely, towards a common centre. 



Stronger evidence that active movements were the cause of the 

 grouping of the swarmspores in the drops was furnished by experiments 

 in which different spores in the same drop were exposed to light from 

 one side ; when some went towards the light, whilst the others 

 removed from it or remained perfectly still. Of the same nature were 

 the results of experiments made with finely divided inorganic sub- 

 stances (amorphous bromine) and with swarmspores which had been 

 killed by heat or by slight admixture with a noxious substance ; they 

 showed none of the movements which were displayed by the living 

 spores in drops of water. 



Having thus settled the general phenomenon, Strasburger pro- 

 ceeded to the special examination of the behaviour of different swarm- 

 spores under light. For this purpose he used chiefly those ot Hcemafo- 

 coccus lacusfris, Ulothrix zonaia, Chcetomorplia acrea, Ulva enteromorpha, 

 lanceolata and ^ compressa, Ulva Lactuca, Botrydium granulatum, 

 Bryopsis pliimosa, CEdogonium and Vmicheria, Scyfosiphon lomeniarium, 

 Chytridium, and Saprolegnia, the swarmspore conditions of Chilomonas 

 curvata and Paramecium, and others. The behaviour of these 

 numerous swarmspores with respect to light was examined under 

 widely differing conditions. He also examined their behaviour in the 

 dark, the effect of heat and other external influences, that of currents 

 * See this Journal, i. (1878) 197. 



