CONTEIBUTTONS FROM THE WISLEY LABORATORY 



377 



may be more or less uniformly attacked (figs. 102 e (a) and 102 f), or 

 covered with scabs. In the latter condition they may bear a super- 

 ficial resemblance to the tumours caused by Chrysophlyctis. 



The processes described above result in severe cases in very con- 

 siderable deformation of the tuber and the appearances presented are 

 very variable (fig. 102 a-d). 

 P The late' symptoms of potato canker are more prominent than the 

 early ones. On this account tubers in a late stage of attack are more 

 usually sent for examination. They are frequently sent some time 

 after they have been removed from the soil. A determination of the 

 organism under these circumstances is not easy. Sometimes the spore- 

 ball powder has fallen away from the tuber so that a microscopic 

 examination reveals only a few yellowish bodies of doubtful character. 

 If spore-balls are present, they are frequently associated with the 

 hyphae of various fungi — the association is so close in some instances 

 that it is difficult to convince- oneself that the spore-balls are not the 

 reproductive bodies of a fungus. 



The papers by Johnson and Mas see respectively contain contra- 

 dictory statements in matters of actual observation relative to the life- 

 history of Spojigospora. Mas see"' claims to have observed the 

 youngest condition of the parasite in the host-cell — the myxamoebse. 

 Johnson,! on the other hand, not only stated that Massee was wrong, 

 having mistaken young starch-grains for myxamoebse, but compared 

 Mas see's figure of m.yxamoebse with one of his own photographs of 

 starch-grains in the potato-cell. I first saw myxamoebae in September 



(1910, and was able to confirm my own observation after a study of 

 microscopic preparations made at the Eoyal College of Science, 

 London, in October. The observation was recorded in a preliminary 

 note on Spongospora published in the Annals of Botany. I In 

 the same number of the Annals, T. G. B. Osborn§ recorded the 

 same fact. Professor J. W. H. TRAHi has also observed the 

 myxamoebse. Mas see's discovery of myxamoebse therefore has been 

 ll amply confirmed. Again, Johnson || pointed out that the spore-balls 

 ' of the parasite were of a spongy texture and not hollow as described 

 and figured by Mas see. U If they were hollow the resemblance would 

 II be closer to the hollow reproductive organs of Berkeley's Tuhurcinia 

 scabies, but Johnson's observation has been confirmed recently by 

 OsBORN** and myselff f; so that in this particular Massee's descrip- 

 Ij tion is incorrect. 



Johnson, 1 1 in the Economic Proceedings of the Boyal Dublin 



* G. Massee, Jour. Bd. Agr., xv. (1908), p. 592. 



t T. Johnson, Sci. Proc. Roy. Dublin Sac, xii. (n.s.) (1909), p. 170; 

 pi. xiii., figs. 3, 4. 



X A. S. HoRNE, Annals of Botany, xxv. (1911), p. 272. 

 § T. G. B. OsBORN, Annals of Botany, xxv. (1911), p. 271. 

 li T. Johnson, I.e. p. 170. 

 H G. Massee, I.e. p. 597. 

 ** T. G. B. OsBORN, I.e. p. 271. 

 ft A. S. HoRNE, I.e. p. 272. 



XX T. Johnson, Eeon. Proc. Roy. Dublin Soe., i. (1908), p. 459. 



