196 PHYTOPHTHORA PARASITICA. 



Ill rare cases two zoospores have been found attached together by a 

 protoplasmic neck (Plate IV, Fig. 6a). The whole mass has been 

 observed to have only two cilia, one at each end. The two zoospores 

 make an effort to get free from each other. They forcibly pull at 

 each other and violently twist round and round the neck, which 

 elongates and consequently becomes thinner. It finally snaps, the 

 zoospores immediately dash away, with a cilium at one end arid a 

 protoplasmic thread at the other. This is probably not a formation of 

 two uniciliate zoospores by the fission of one bi-ciliate swarm spore, 

 as found by Atkinson in Artotrogus (Pythium) intermedins (de Bary) 1 ; 

 but merely an incomplete breaking up of the original protoplasm in 

 two units of zoospores. In Atkinson's case the movement of the 

 bi-ciliate zoospore becomes slower five or ten minutes after discharge 

 and " finally it nearly ceases and the body undergoes plastic move- 

 ments resembling somewhat that of an amoeba. At first this 

 amoeboid movement is irregular, but after a few minutes it assumes 

 a definite character which tends to cut the organism into two." His 

 figures show that the bi-ciliate zoospores have a single vacuole. 2 

 What I have found is the appearance of two distinct units connected 

 by a narrow neck at the time of discharge, each unit possessing a 

 vacuole (Plate IV, Fig. 6a) ; the whole mass being almost twice 

 the size of a normal zoospore ; its movement is at no stage 

 " amoeboid," and the two units get separated by the snapping off 

 of the protoplasmic neck, the result of the hard pull that they have 

 at each other. I have found two units thus united together 

 hardly half a dozen times while Atkinson has found the breaking 

 up of bi-ciliate zoospores into two uniciliate ones taking place as 

 a rule. In one case, along with normal zoospores, a motile mass of 

 protoplasm was discharged from a sporangium at 10-15 a.m. 

 (Plate IV, Fig. 26). Its shape was that of a roughly drawn pentagon 

 with a distinct cilium at each of its angles. It whirled round and 

 round a single point as if one of its cilia, which was not visible, had 



1 Atkinson, Geo. F. Damping off, Cornell Univ. Agric. Expt. Stat. Bull. 94, Bot. Division, 

 1895, p. 249. 



2 Ibid., pi. II, fig. 24, p. 247. 



