378 JOTTRNAL OF THE ROYAL HORTTCTTLTTTRAL fiOCTETY. 



Socieiy, gives the following description of the probahle hehavioiir of 

 Spongospora in the potato plant: — "Keeping in mind whaii is known 

 of the mode of life of other slime-fungi, the life-historj^ of Spongospora 

 seems to be very much as follows : — • 



A scabby potato is planted and sprouts. The stored solid proteid Iji 

 fcrystalloids) and carbohydrate bodies (starch grains) in the tuber n 

 become diffusible. The resting plasmodium of Spongospora in the 

 host-cells becomes at the same time actively motile, and feeds in the 

 now available organic food-materials of the host-cells. As the potato 

 eye sprouts and forms a shoot, the parasitic plasmodium passes into it. 

 The shoot develops and gives off branches and tubers into which the 

 parasitic plasmodium passes, living on the host-cells' contents in its 

 passage. In the growing tuber the plasmodium luxuriates. As the 

 tuber ripens, with loss of water and solidification or precipitation of its 

 stored organic matter, the plasmodium creeps towards the surface of 

 the tuber and becomes converted into spore-balls, usually one in each 

 host-cell. The spore-balls raise the skin of the tuber, which peels off, 

 leaving exposed a wound full of spore-balls." 



Johnson's description of 1908 * refers to the probable behaviour of 

 the parasite in the potato; in 1909, f however, the impression is con- 

 veyed that the life-cycle of Spongospora had been actually determined. 

 " The Plasmodium, too, carries the disease from the seed-tubers through 

 the stoloniferous branches over into the new tubers, making them 

 scabby as I have already shown." This sentence refers apparently to 

 experiments described in 1908| and 1909. § — "In 1905, I planted a 

 scabby tuber and found the crop scabby, indicating that the disease 

 passes from the seed-tuber to the new crop of tubers as a plasmodium, 

 through the haulm and branches of the rhizome. I have seen tlie | 

 scab on a rhizomatous branch itself " (1908); and, " I planted healthy 

 tubers of * Sutton's Superlative,' into which I had previously grafted a 

 wedge of a scabby tuber, from which all the spore-balls, so far as I 

 could make out, had been scraped off. The tubers formed were 

 scabby. Thus it appears that the resting plasmodium can com- 

 municate infection to healthy tubers " (1909). These experiments, 

 however, absolutely fail to demonstrate the peculiar behaviour of the 

 parasite ascribed te it by this author. Massee || states : " It is highly 

 probable that the plasmodium in the scabbed potatos become encysted 

 during the winter months, and resume their activity when the potatoes 

 commence to sprout." He has, however, brought forward no con- 

 vincing evidence in support of this view. It has been already pointed 

 out that the distribution of Spongospora in the tuber can be easily 

 seen on cutting the tuber open. The line of demarcation between the 



* T. Johnson, Ic. p. 459. 



t T. Johnson, Sci. Proc. Roy. DxiUin Soc, xii. (n.s.) (1909), p. 171. 



t T. Johnson, Eco7i. Proc. h'oy. Dublin Soc, i. (1908), p. 458. 



§ T. Johnson, Sci. Proc. Dub. Soc, xii. (n.s.). (1909), p. 173. 



11 G. Massee, Jour. Bd. Agr., xv. (1908), p. 592.— This paper is without the 

 author's name, but it is quoted in Diseases of Cultivated Plants and Tr^.es, 

 p. 532. 



