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THE FARMERS HANDBOOK. 



appearance of normal, healthy, vigorous plants, and are very liable to develop 

 brittle stems that break off in a very moderate breeze. The stems of all 

 such plants, when cut sharply across just above the root, show a ring of 

 sap-conducting tissue that is discoloured — it is brown or black. Cutting the 

 stem across at intervals, this discoloured tissue may be traced upwards 

 towards the apex. The colour becomes fainter, but it can be traced even 

 with the naked eye into the veins of the big leaves. In the neighbourhood 

 of this discoloured tissue cells containing bacteria are found. They exist in 



Fig. 5.— a A young tobacco plant that is diseased showing the characteristic bulbous appearance at the 

 base of the stem. 5 Young diseased tobacco plaat which has started to lengthen and the bulbous 

 swelling at the base base is diminishing. 



such numbers that there seems good reason to suppose that they are connected 

 with the discolouration and the diseased condition. The stems of infected 

 plants swell and become tumid (sometimes almost bulbous) immediately above 

 the roots. If the plant remains short and swollen it is regarded as being 

 worthless for planting out, but if, as sometimes happens, it begins to lengthen 

 and lose its swollen appearance, it may be worth transplanting, though it 

 never fully recovers. A plant showing the abnormal swelling is shown at 

 Fig. 5, a, and one that is lengthening and recovering is shown at Fig. 5, b. 



