THE GBKEN CELLS OF CONVOLUTA ROSCOFFENSIS. 179 



(2) At this stage it has no germ of infection within its body. 



(3) Infection occurs normallywithin three daj^s of "birth." 



(4) Water taken from the shore — not necessarily in the 

 neighbourhood of Convoluta-patches — contains the infecting 

 organism in such numbers as to induce wholesale infection in 

 large batches of larvte. 



(5) The infecting alga habitually settles down and de- 

 velops on the egg-capsules, which therefore serve as sources 

 of infection (see also Keeble and Gamble, 1905). 



(6) Infection does not take place directly or indirectly from 

 the body of the pareut. 



(7) The green cells of an adult Convoluta are incapable of 

 life apart from the body of the animal. 



(<S) Consequently the association must be regarded, not as 

 a symbiosis, but as a case of parasitism, the host being the 

 green cells and the parasite Convoluta (see also Section VI). 



Section III. The Isolation op the Infecting Organism 

 AND THE Synthesis op the Green Convoluta. 



It is natural that, in seeking to isolate the infecting 

 organism of Convoluta, effort should be directed first toward 

 the cultivation of green cells obtained from the body of the 

 green animal. Haberlandt (1891) was the first to attempt 

 this. His efforts were unsuccessful. We have attempted it 

 again and again, but have failed. Miss Harriette Chick, who 

 lias had much experience in such work, was good enough to 

 make in the laboratory at Tregastel in 1905 a large number 

 of culture experiments, using a great variety of nutrient 

 substances in liquid and solid media. The experiments gave 

 no positive result. These failures make it in a very high 

 degree probable that the task is impossible, and so lend some 

 support to the conclusion arrived at in the preceding section 

 that the green cells of Convoluta, once developed within 

 the body of that animal, are no longer capable of separate 

 existence. 



It became necessary, therefore, if the search for the 



