CONTRIBUTIONS FROM THE WISLEY LABORATORY. 609 



them through lengthwise, beginning at the stalk or " heel " end. Those 

 with the very least trace of spot, blotch, or streak were rejected in 

 selecting disease-free tubers. Hence only half-tubers were planted. 

 Lots E and F were selected from the disease-free tubers given by 

 Messrs. Sutton, tested as above, and planted as a control. 



Washing was carried out by thoroughly rinsing the half-tubers with 

 tap-water ; the sets were then allowed to dry. The washed lots are 

 those marked C, D, and F in the Table. 



Table I. — Experiments with Potato ' Duke of York,' 191 2. 



Whence obtained 



Whether diseased 

 or not-diseased 

 half- tubers were 

 planted 



Whether sets 

 were washed 

 or not 



Numbers 

 of rows 



Number of 

 sets planted 



Total 



weight of 

 crop 



Reference 

 number 



From / 



Diseased 



Not washed 



ij 2, 3 



72 



63 lb. 



A 



experimental 1 



Diseased 



Washed 



4> 5, 6 



72 



52 „ 



C 



plots in 



Not diseased 



Not washed 



7> 8, 9 



72 



80 „ 



B 



Scotland I 



Not diseased 



Washed 



10, 11, 12 



72 



88 „ 



D 



Messrs. Sutton, 1 



Not diseased 



Not washed 



13, M,i.5 



72 



85 „ 



E 



Reading ( 



Not diseased 



Washed 



16, 17,18 



72 



85 „ 



F 



The tubers were planted, in April, in light sandy soil previously 

 treated with a little artificial manure, and lifted at the end of 

 August. They were then stored in boxes for the winter. A number 

 of the tubers of each lot were tested from time to time, some immedi- 

 ately after lifting, others at various intervals. The result of the 

 examination of tubers from September 1912 to January 20, 1913, 

 is shown in Table II. Here" we see that streak had appeared, but only 

 in lots A, C, and B, and blotch in lot F. Phytophthora occurred in all 

 except lot A, but no cases of dry rot are recorded. 



Table II. should be compared with Table III., in which the 

 results are recorded from January 20 to April 1913. There is no evi- 

 dence to show that streak had increased during the winter, whilst the 

 percentage of blotch is apparently less. This percentage, however, is 

 probably less than it should be, since some of the tubers would become 

 infested with Fusarium, shrivel up, and be recorded as cases of dry 

 rot. It will be noted that seven per cent, of the tubers are classified 

 under dry rot, as against none at all in Table II. 



Table II. — Experiments with Potato ' Duke of York.' 



Result of examination of tubers from September 1912 to January 20, 1913. 



Reference 

 letter 



Number 

 of tubers 

 examined 



| Streak 



Phyto- 

 phthora 



Blotch 



Dry rot 



Total 







1 



a 



in 



Perce 

 ■ 1-1 



ii 



s-a 



utage 



0 

 0 



s 



Total j 



A 



IOO 



6 



0 



O 



O 



6 



6 



0 



0 



6 



C 



258 



39 



.9 



O 



O 



48 



15 



3-5 



0 



18-5 



B 



280 



11 



3 



O 



O 



14 



4 



1 



0 



5 



D 



206 



0 



0 



O 



O 



0 



0 



0 



0 



0 



E 



140 



0 



9 



O 



O 



9 



0 



6-4 



0 



64 



F 



184 



0 



13 



16 



O 



29 



0 



7 



9 



16 



VOL. XXXIX, 2 8 



