for the Groicth of Undiseased Potatoes. 
383 
Table III — Showing the Number of apparently Diseased Setts 
Planted and of Plants that grew from them, in the Expebimental 
Plots on Mr. Spencer's Farm, Essex. 
No. 
DiS6£lS6il 
Tubers 
JTUUlUiU. 
Plants 
Grew. 
1 
Earl}' . . 
0 
0 
2 
75 
3 
3 
Late . . 
14 
5 
4 
6 
3 
5 
2 
0 
6 
)» ■ • 
0 
0 
I learned from Mr. Spencer that he had in previous years 
experimented with diseased seed-tubers with the view of deter- 
mining the relation of their products to the disease; and he 
had observed that the plants grown from them were not more 
liable to be attacked by the disease, or to suffer from it, than those 
grown from healthy tubers. The aspect of the eleven plants, 
when I visited the experimental plots in Essex in the end of July, 
corroborated Mr. Spencer's conclusions. This is of considerable 
value in relation to the yet unsolved question as to how the fungus 
causing the disease maintains its existence from the autumn to 
the following July or August, when under favourable circum- 
stances it suddenly appears and spreads with wonderful rapidity. 
It rather tells against the opinion that the life of the fungus is 
maintained by planting diseased tubers ; for instead of the dis- 
ease appearing first in the plants produced from them, these 
plants suffer only along with, and in the same proportion as, their 
neighbours produced from healthy seed. On the other hand, it 
must be remembered that if the mycelium of the parasitic fungus 
developes in a single plant grown from a diseased tuber, and this 
mycelium fructifies, the enormous mass of seed which is rapidly 
produced and reproduced under suitable conditions, would fully 
explain the spread of the disease. We look forward with much 
hope to the observations and experiments that Professor De Bary 
is now prosecuting for light on this obscure part of the history 
of the potato fungus. 
In the stations in the south and east of England, and the south 
oi Ireland, all the seed-tubers were in the ground befoie the close 
ot the month of March ; in the north and west of England, in 
Scotland, and in the north of Ireland, they were all planted before 
the middle of April. 
The information obtained from the growers, or observed during 
