166 Scientific Proceedings, Royal Dublin Societij. 



roll from other diseased plants. It should be explained that the time of onset 

 of rolling of the leaves varies considerably, even in adjacent similar plants. The 

 comparative examinations were repeated six times from May 25 to June 8, the 

 variety used throughout being British Queen. As a general rule, corresponding 

 leaflets from three plants of each category were used in each examination. They 

 were removed at 5 p.m., and kept in the dark with their cut ends in water for 

 from sixteen to forty hours, and were then submitted to the iodine test in the 

 usual way. 



The results of all the examinations may now shortly be summarised. In 

 the first trials, on May 25, 26, and 27, there was no noticeable difference in the 

 amount of starch present in such leaflets as came from healthy or diseased (but 

 normal looking) plants after being kept in the dark for sixteen hours. Leaflets 

 which had already begxin to roll at this time, however, showed excess of starch ; 

 and the more pronounced the rolling the greater was the amount of starch 

 present. On May 30 there was clearly more starch in leaflets which had not 

 begun to roll, but which were taken from diseased plaiits, than in similar 

 healthy leaflets, both being kept sixteen hours in the dark. When, however, 

 the leaflets were kept in the dark for forty hours, there was no difference 

 between the two lots. This shows that although starch accumulation in the 

 diseased leaves had begun, it had not j^et reached very large proportions. 

 Confirmatory results were secured in the case of leaves from diseased plants 

 which were tested on June 2. The last examinations, carried out on June 7, 

 when the majority of the plants in the plot already exhibited symptoms of 

 leaf-roll, showed a still more striking accumulation of starch in diseased lower 

 leaves which had not yet begun to roll as contrasted with similar healthy leaves. 

 In this case the difference was still easily perceptible after the leaves had been 

 kept forty hours in the dark. This indicates that the amount of starch present in 

 the diseased leaves had increased. 



Corroborative results were secured by systematic microscopical examination 

 during the same period of bleached material taken from the plant in the 

 morning (10 a.m.), the diseased leaves being taken from the same plant 

 throughout. Up to June 2 there was no perceptible difference between the 

 diseased but non-rolled plants and healthy plants. The leaves of both contained 

 about the same amount of starch, the lower ones being generally empty except 

 for the guard-cells and "starch-sheath," and the upper ones containing a good 

 deal of starch throughout the mesophyll. The first sign of increased starch- 

 content in the diseased but non-i'olled lower leaves was noticed on June 3. 

 This feature had become veiy pronounced by June 6, there being by this time 

 very much more starch present in the morning in the lower leaves (which had 

 not yet rolled perceptibly) than in the ixpper leaves of the same plant. 



A general examination of diseased plants showing the earliest symptom of 

 rolling was made at this period in comparison with healthy plants, the material 

 being collected at 10 a.m. and examined at once. The diseased lower leaf- 

 blades contained an abnormal amount of starch, while their petioles were not 

 distinguishable from those of healthy plants, both containing starch only in the 

 ' ' starch-sheath. ' ' This was also the ease in the stems, but here there appeared 

 to be appreciably less starch present in the "starch-sheath" of the diseased 

 plant than in that of the healthy one. ^ No necrosis of the phloem was seen in 

 any part of the plants, although a careful search was made. 



Although the methods used in the experiments described are not altogether 

 free from objection, for the reason that the rolling of diseased leaves sets in 

 gradually, thus rendering it impossible to say exactly when it begins, and 

 because rolling follows rapidly after the beginning of starch accumulation, 



