182 F. KEEBLE AND F. W. GAMBLE. 



Section IV". The Life-history op the Infecting Okganism. 



The green spherules from which the swarms of flagellated 

 cells issued as described in the preceding section served as a 

 startiug-point for the cultivation of the green alga which, as 

 just shown, is the source of the green cells of Convoluta. 

 The securing of material for this purpose was rendered com- 

 paratively easy owing to the Avell-marked positive photo- 

 tropism of the alga in its motile stage. Issued from the 

 egg-capsule, the flagellated cells swarm toward the more 

 brightly illuminated side of the vessel in which they are con- 

 tained; there they settle down sooner or later, either singly 

 or in pairs, along and just above the water-line. Thus the 

 position of the algae is marked by a visible green patch. 

 This patch consists of numbers of flagellated cells, and also 

 of many which, having withdrawn their flagella, have sur- 

 rounded themselves with a well marked and often stratified 

 wall. A sample from such a patch was transferred by means 

 of a platinum loop to a vessel containing filtered sea-water, to 

 which a little potassium nitrate had been added, and in which 

 had been placed a number of empty egg-capsules. After 

 some days a green streak along the water-line made its 

 appearance on the brighter side of the vessel. The vessel 

 was taken from Tregastel to England (Reading) in September, 

 1905, placed in tlie light in a cool incubator, and kept under 

 observation. The green scum gradually disappeared, and it 

 was feared that the organisms had died. Toward the end of 

 May, 1906, the vessel was placed on a bench in the laboratory 

 in a good light, and within a fortnight a green scum re- 

 appeared on the illuminated side of the vessel. Microscopic 

 examination showed the identity of the organisms constituting 

 this scum, with those added to the water the previous year. 

 Beside the green layer on the side of the vessel loose masses 

 of pale green mucilage, floated up to the surface by reason of 

 included gas-bubbles, made their appearance. Imbedded in 

 these mucilaginous masses were numbers of quiescent green 

 cells, lying singly, in pairs, or in groups. 



