172 i\ KEKBLE AND F. W. GAMBLE, 



Erauce ; in the Zoological Department, Victoi-ia University, 

 Manchester, and in the Botanical Laboratory, University 

 College, Reading. 



We acknowledge with gratitude the assistance we have 

 derived from a grant made by Section D of the British 

 Association for the purposes of this investigation. 



Section II. Proof of the Oeigin of the Geeen Cells by 



Infection. 



The dark spinach-green colour of Convoluta roscoff- 

 ensis is due, as is well known from the descriptions of 

 von GrafE (1905-1906), Geddes (1879, 1879 a, 1882), Haber- 

 landt (1891), and ourselves (1903), to dense layers of green 

 cells. These green cells are distributed with great uniformity 

 in the body, and extend from just below the epidermis into 

 the deeper tissues. Only in the anterior end of the body, in 

 front of the otocyst and rudimentary eyes, are the green cells 

 so few in numbers as to reveal the whitish colour of the 

 animal. 



The general appearance of an adult Convoluta, Avhen 

 examined microscopically, is not unlike that of the mesophyll 

 of a green leaf. In surface view the green cells are flat, 

 somewhat variously shaped bodies, now of rounded outline, 

 now drawn out at one end into long tail-like extensions which 

 appear to connect cell with cell. 



The individual cells, described by Haberlandt (1891) in his 

 important contribution to our knowledge of the green cells 

 of Convoluta, are naked protoplasts, the larger part of each 

 of which consists of a more or less cup-shaped chloroplast 

 containing a large polygonal or irregular pyrenoid. The 

 small remaining part of the protoplast is colourless, and lies 

 either in the hollow cup-like invagination of the chloroplast 

 or, when the shape of this latter is irregular, excentricaliy. 



Though often fi-ee, or almost free, from starch, the green 

 cells may, under certain conditions, contain considerable 

 quantities both of pyrenoid starch — that is, starch distributed 



