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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



tests for the presence of solanin in vegetable tissue, the results of the 

 tests described in this paper indicate a greater quantity of this alkaloid- 

 gluooside in the diseased than in the healthy areas of a given potato. 

 If this be the case, an attractive explanation of the phenomenon of 

 bruise may be suggested. We may suppose that there are three 

 periods in alkaloid metabolism, as well as three periods in 

 carbohydrate metabolism, in potato — one, say, in late summer and 

 autumn, of production of alkaloid-glucoside (solanin) from alkaloid 

 (solanidin) and sugar; then a resting period; and, thirdly, a time — 

 say, in spring — of hydrolysis of the alkaloid-glucoside into sugar and 

 alkaloid — the latter being made innocuous by processes which can occur 

 in this period, but not in the first period. Imagine that for some reason 

 or other the process of alkaloid-glucoside formation receives a check 

 causing reversal; or, that the process of alkaloid-glucoside hydrolysis 

 sets in too early, when the alkaloid formed could not be rendered 

 innocuous; then the released alkaloid might act injuriously upon the 

 cells in which the abnormal metabolism is taking place and constitute the 

 cause of the injury to the tissue. It will be remembered that, in testing 

 the diseased tissue, only slightly affected areas were used, so that the 

 increased amount of alkaloid is apparent in the incipient stages of the 

 disease. This point perhaps adds weight to the argument. There 

 are in the potato a large number of internal vascular bundles, so 

 that the starch-parenchyma is well supplied with conducting tissue, 

 and the emptying of the store of reserve carbohydrate would take place 

 fairly uniformly. One might expect that an interference with the 

 normal process of alkaloid-glucoside hydrolysis would disturb this 

 translocatory system. It is strange, however, that the affected areas 

 should occasionally be localized to the starch-parenchyma between the 

 principal bundle cylinder and the cork, and that they are infrequently 

 found generally distributed in the internal starch-parenchyma. 



The whole matter might be approached from an entirely different 

 point of view. We might ' suppose that the cells are progressively 

 poisoned by bacteria. The poisoning might spread slowly in the tissue 

 from some given centre, or the effect might be produced at some little 

 distance from the source of irritation. In two cases which have been 

 included with the consideration of typical bruise, the disease appeared 

 about the principal vascular cylinder. A series of stages was obtained, 

 ultimately involving almost the whole interior of the tuber. It might 

 appear clear to some that this phase of the disease is due to the slow 

 action of bacteria spreading inwards from the bundles; but it might 

 also be indirectly due to the condition of the bundles themselves. 



The negative evidence of the presence of bacteria obtained from a 

 microscopic examination, and the failure to cause the disease to spread 

 and to isolate pathogenic bacteria perhaps count for very little. But 

 the whole evidence, considered collectively, is decidedly against attach- 

 ing much imfortance to a possible organism factor in relation to the 

 disease. Even in bacterial diseases of potato recently described it is | 

 doubtful whether the bacteria are the primary cause of the disease. 

 Pethybridge, in Ireland, has isolated bacteria which cause the effect 



