TflE GRERN ORLLS OP OONVOLUTA ROSOOFFENSIS. 183 



Sabciilfciires in various media were made from this material. 

 Some of these were taken back again to Tregastel in the 

 summer of 1906, and proved snfficient for the infection of 

 colourless young Coavolutas. The cultures have also served 

 to demonstrate that the alga which infects Convoluta ros- 

 coffensis has a very varied liFe-histoiy. In the first place, 

 the active flagellated cells are dimorphic. The macrocytes, 

 16 /x in length (figs. 4, PI. 13 and 12 a, PL 14), are nearly 

 double the size of the microcytes (4 : 2*5) (figs. 3, PI. 13 

 and 12 b, PI. 14). Except in point of size the large and small 

 cells are similar in their histological details. 



Both the large and small cells have four equal ilngella 

 arising from the anterior colourless part of the protoplast. 

 The flagella in both bear the same relation to the length of the 

 body (2:1). In both the chloroplast is cup-shaped, the pyrenoid 

 single, the eye-spot lateral and situated in the anterior half of 

 the cell. In both the wall is extremely delicate and gives no 

 cellulose reaction — e. g. with sulphuric acid and iodine or 

 with Schultze's solution or calcium chloride-iodine; but with 

 zinc chloride-iodine it gives a faint rose-colour (chitin reaction) . 



The nucleus — a description of which is given in Section V, 

 where a comparison between the free and imprisoned cells is 

 di'awn — lies, in both large and small colls, in the colourless 

 part of the protoplast which fills the hollow of the cup-shaped 

 chloroplast. It suffices to say here that the nucleus is sus- 

 pended in a layer of the protoplast from which run strands, 

 two downwards, serving as slings for the pyrenoid, and 

 others outward through the chloroplast at regular intervals to 

 meet the thin, colourless layer of protoplasm which forms a 

 pellicle around the exterior of the chloroplast. 



Large and small cells are alike equally phototropic, and 

 both settle down after a period of activity, Avithdrawing their 

 flagella and surrounding themselves with a more or less thick 

 mucilaginous wall. The wall may form with great rapidity, 

 so that encysting macrocytes are often to be met with whose 

 flagella may be seen in undulating movement within the 

 enclosing wall. 



VOL. 51, PART 2. — NEW SERIES. 15 



