I907-] 



Potato Leaf-curl. 



467 



of growth by February at the latest, and in a mild winter 

 shoots will be showing before Christmas. If no indications 

 of growth appear by March, a number of sets should be taken 

 from different boxes, and the lower part cut off ; it will be 

 found, probably, that there is a brownish streak or ring per- 

 meating the flesh, and if this is general the stock should be 

 rejected without hesitation. 



It is important to consider the possibility of the sets being 

 infected before planting so that time and money may not 

 be spent in the preparation of ground that cannot possibly 

 give a satisfactory crop. Growth in the seed tuber in the 

 store is not, it is true, certain evidence of full vitality. The 

 writer has had instances of curl attacking a crop when the 

 seed employed had shown satisfactory signs of vigour in the 

 boxes, but this points to the presence of fungus spores in the 

 soil or in the tuber as hybernating mycelium.* Treatment 

 of the seed, however, on the lines indicated favours the chance 

 of a good crop, even if it does not absolutely ensure it in all 

 instances. 



Change of Seed. — Experience shows that cases of failure 

 are most common and most severe where stocks of the 

 same seed have been held year after year. These stocks 

 will frequently sprout in the store, but will fail to resist any 

 disadvantageous circumstances, such as chilled soil or lurking 

 spores, out of doors. The superior vigour which fresh stocks 

 possess gives them a better chance of battling with natural 

 disadvantages. I have made some experiments with a view 

 to proving the advantages of change (1) by planting home 

 stocks which have made good growth in the store, in ground 

 from which a " curled " crop had been taken the previous 

 year, and (2) by planting on similar ground corresponding 

 seed from a fresh source. The former has been badly curled, 

 and the latter completely immune. This is an example of the 

 fact that thoroughly vigorous stocks of seeds are capable- of 

 resisting the risk of contagion. They are also able to over- 

 come in some degree such natural disadvantages as poverty 

 of soil and unsuitability of position. 



Over- maturity . — It is only within comparatively recent 

 years that the question of over-maturity has been treated as. 



* Ci. Journal of the Board of Agriculture, Vol. xiii, August, 1906, p. 257. 



2 G 2 



