REPORT OF THE BOTANIST 255 



SESSIONAL PAPER Tno. 16 



Sixteen bushels have been considered to be planted on an average per acre. The 

 legal weight per bushel of potatoes, i.e., 60 pounds, has been taken in making these 

 calculations. Thus it would appear from the above table that the Carbonate of Soda 

 lot yielded heaviest and the Formalin lowest, the latter, however, reducing the liability 

 to scab considerably. The other treatments seem to act alike with the untreated ones. 

 We are by no means satisfied to recommend the Formalin treatment for scab from our 

 results obtained. Various conditions may have influenced the growth of potatoes 

 and have resulted in a comparatively large reduction of the yield of Formalin-treated 

 tubers. It will be interesting to see the results obtained by next season's experiments 

 on the identical lines. This table again proves that no reliable conclusions can be 

 drawn from a single experiment. 



INTERNAL SPOTTING OF POTATO TUBERS. 



(Plate II. b). 



Attention has been paid during the year to samples of a potato trouble received 

 from various sources. The potatoes appeared perfectly sound externally but showed 

 on cutting them, towards the stem end, a curious brownish ring consisting of a large 

 number of isolated, minute specks corresponding to the vascular system of the tubers. 

 On peeling the tubers rather thickly, the brownish discolouration became apparent 

 in narrow, branching streaks. Microscopical examination revealed that only the vas- 

 cular bundles of the tubers were discoloured. In no case did this discolouration extend 

 to the other end of the tuber. Its appearance is quite different from the Fusarium 

 Rot, (Fusarium oxysporum), with which it is generally confused. In this case, the 

 appearance of the discoloured portions, though within the region of the vascular system, 

 extends into the tissues surrounding these bundles and the discolouration also appears 

 rather blackish or sometimes bluish-brown. Microscopical examination also invariably 

 reveals mycelial threads of a fungus within these tissues. 



Some of the spotted tubers were planted on plots on the experimental ground and 

 the plants were watched throughout the season. No difference was noticed in the case 

 of the plants developing from the affected tubers from plants grown from selected 

 sound tubers. On harvesting the tubers, they were found quite free from any sign 

 of spotting and they were quite normal as regards yield. A single tuber was raised 

 in sterile soil and behaved in the identical manner — the tubers produced showed no 

 discolouration. Potato tubers similarly affected were again sent early in spring to 

 ascertain whether they could be used for seed. Our experience has shown that such 

 tubers may produce a sound crop, but is limited to one year only. We would not 

 advise in any case the purchase of affected potatoes for seed. Some physical condition 

 may set in, which may change this aspect considerably. Farmers are advised, when 

 buying potatoes for seed, to cut a thin slice off at the stem end, — should any discolour- 

 ation become visible, the tubers should not be used. The matter of these discoloured 

 tubers was discussed with some plant pathologists of the United States. They also 

 have observed identical cases and confirm our observations as regards the absence of 

 any micro-organism. ' Apparently,' one observer states, ' the spots are due to the 

 collapse and death of the tissues from undue withdrawal of moisture.' In the exper- 

 ience of the American investigators, this phenomenon is identical with the rust-like 

 spots of collapsed tissues frequently observed in potato tubers. This spot is also well 

 known in Europe, where it has received the names ' Sprain ' (England) and ' Eisen- 

 fleckigkeit' (Germany). The microscopical observations of the diseased tissues 

 recorded in the various European countries agree with those on this side of the 

 Atlantic, and nearly all observers agree that the phenomenon is a physiological 

 one. The microscopical appearance, especially of some of the spots observed, very 

 closely resembles the so-called Baldwin Spot or Bitter Pit of apples. The most recent 

 investigation of this trouble appears to have been made by A. S. Home (Ann. Mye. 



