68 On the Infecting Organism of Convoluta roscoffensis. 



Ordinary sea-water or such cultures alike induce infection within a few 

 days, when added to just hatched Convolutas reared previously under sterile 

 conditions ; whereas the addition of sterile sea-water to samples from the 

 same stock of Convoluta produces no infection. 



3. Mature of the Infecting Organism. — Whilst reserving for a detailed and 

 illustrated account the full description of the organism infecting Convoluta 

 roscoffensis, we may here briefly refer to its more salient characters and 

 systematic position. In its adult and holophytic stage, the motile green 

 organism is ovoid and flattened in front. At the anterior end it possesses 

 two pairs of similar flagella. A basin-shaped chloroplast envelops the greater 

 part of the body, and is turned in anteriorly, forming a clear border to a 

 colourless funnel-shaped area which runs axially for a third of the cell's 

 length. A plate-like red " eye-spot " or stigma, with a darker rim, lies 

 somewhat excentrically a little in front of the middle of the cell and not in 

 relation to the flagella. The resting nucleus is spherical. Near the posterior 

 end of the chloroplast is a large octagonal pyrenoid, provided with a starch 

 sheath, giving it a somewhat irregular outline. True starch, giving a marked 

 blue colour with iodine, is present in quantity. A cell-wall is either absent 

 or of extreme tenuity in the organism when first liberated, hut later on a 

 marked wall of mucilaginous character is demonstrable and may reach a 

 considerable thickness. 



These characters indicate that the green cells of Convoluta roscoffensis are 

 true algae, belonging to the Chlorophycese and allied to Chlaviyclomonas. The 

 presence of four equal flagella suggests that they helong to the genus 

 Carteria* 



* Blackmail and Tansley, ' New Phytologist,' vol. 1, p. 23, 1902. 



