138 Scientific Proceedings, Royal Dublin Society. 



I have never seen the enveloping extruded membrane mentioned, in any 

 fresh, ruptured sporangium. The wall ruptures; and tlie zoospores escape 

 without any sign of the extrusion of a membrane. This is not, however, the 

 ease in artificially preserved material. I hardened a rotting piece of potato- 

 wart, kept for some time under cultivation in potato-juice, and full of resting 

 sporangia, in Flemming's solution, and then stained it by tlie three-colour 

 method. On squeezing under the microscope a sporangium isolated from the 

 general mass, its outer wall burst, and the contents as separate zoospores were 

 extruded, enclosed by the inner wall as a liyaline membrane (PI. IX., fig. 7). 

 The persistence and protrusion of the inner wall as a membrane thus seem to 

 be due to the artificial preservation of the same by reagents. If the existence 

 of this protruding membrane in nature could be accepted, it would not indicate 

 Synchytrium affinities. The membrane in Synchytrium is an external one, 

 and envelops a sorus of 150 or more sporangia. It is quite different from 

 the inner wall of the single sporangium. This no more protrudes in Synchy- 

 trium than in Chrysophlyctis. My figure of the sporangium is, iu all 

 essentials, like that of Synchi/triiim taraxaci (fig, 8e), figured by A. Fischer (9). 

 His figure 8c (p. 46, o.c.) shows the membrane enveloping the sorus of 

 sporangia in S. Mercurialis. 



Prevention of the Disease. 



It is stated that the disease first appeared in 1896 in Birkenhead district, 

 and that it was brought there iu Coutiuental cattle-boats. It is now found 

 in many different districts in England, Wales, and Scotland. It is often so 

 pronounced as to destroy the whole crop, and it is not confined to garden-plots. 

 Warty tubers are naturally poorer in food-matter than healthy oues, and 

 when not destroyed in the field do not keep well in store. They ought to be 

 destroyed as soon as found, and on no account saved for seed. The most that 

 can be done with them is to boil and feed them to pigs. The haulms should 

 be gathered and burnt. Infected laud should be kept free from potatoes for 

 possibly seven years. Tiie applioatiou of kainit or other potash-manure 

 and of phosphates, the close inspection of seed-tubers, and the avoidance of 

 low-lying or undrained land should prove beneficial in preventing a recurrence 

 of attack. In keeping with the known aquatic habits of the Chytridiacese as 

 a group, a wet undrained potato field would be a predisposing cause, favouring 

 the spread of potato-wart. This is true of flas-yellowing duo to Asterocijstis 

 racUcis Wilde., of lucerne-canker in South America, due to Urophlyctis alfalfw, 

 and of cabbage black-leg due to Ol2:)idiuni brassicce iu North America, all diseases 

 caused by Chytridiaceie. Curiously enough, I have seen only one reference 

 to the bearing of the condition of the soil on cases of potato-wart, and have 



