168 Scientific Proceedings, Royal Dublin Society. 



the occurrence of a peculiar upward rolling of the blades of the leaflets of the 

 upper leaves, and within three days this feature was verj- marked on the four 

 treated plants. The four untreated controls remained quite normal (figs. 1 and 2, 

 PI. VI). The rolled leaves of the treated plants still retained their dark green 

 colour; and tests of their starch-content made on the third day after treatment 

 showed an accumulation of starch after they were kept in the dark for forty 

 hours with their stems in water. This excess became more pronounced as 

 time went on. On the seventh day, for example, the "artificially" rolled top 

 leaves, when removed from the plants in the evening, contained olsviously more 

 starch than corresponding normal leaves taken from the untreated control plants. 

 The starch disappeared from the normal leaflets when kept in water in the dark 

 within sixty-four hours (perhaps in a shorter time), but within this period the 

 similarly treated rolled leaflets had only cleared slightly at their tips (fig. 6, 

 PI. VI). In seven days not more than one-quarter of the area of the "artificially" 

 rolled leaflets Avas free from starch, the clearing proceeding from the tip down- 

 wards (fig. 7, PI. VI). An actually diseased and rolled lower leaf from an 

 affected plant, kept at the same time under the same conditions, began to clear, 

 however, at its hase. Similar results were obtained on the seventeenth day of 

 the experiment, when whole leaves were used in place of leaflets. 



The presence of an abnormal quantity of starch in the "artificially" rolled 

 leaves was confirmed hy microscopical examination. The excess of starch was 

 not confiaied to the lamina of the leaf, but was also very noticeable in the 

 parenchyma, and particularly in the "starch-sheath," of the petiole, in which 

 the starch gTains were unusually large. 



Up to the seventeenth day after excision the treated plants remained in the 

 condition described, but the rolling had gradually become more pronounced (see 

 photograph made on the seventeenth day, reproduced in fig. 3, PL VI), and had 

 extended downwards on the plant so as to involve practically all the leaves but 

 the lowest. At that time these plants presented a marked contrast with their 

 controls. The sjTnptoms of rolling obviously differed from those which 

 accompany primary leaf -roll, the most pronounced distinction being the fact 

 that the "artificially" rollecl leaves retained a very dark green colour, and 

 showed a tendency on the part of the leaf as a whole to curve downwards. On 

 the seventeenth day, however, one of the treated plants showed suspicious 

 symptoms of true primary leaf -roll," and it was immediately cut off at ground- 

 level in the hope of preventing the infection of the remaining three healthy 

 plants, from which it was desired to secure healthy tubers or cuttings. The 

 soil, therefore, which had previously been removed, was heaped up about the 

 bases of the stems of these plants, and they were allowed to grow in the normal 

 way. 



The hope of keeping them in a healthy condition was, however, only partially 

 realized. Primary leaf-roll continued to appear in plant after plant, both 

 treated and control, and each plant was removed as it became infected. On 

 the twenty-fourth day of the experiment only three plants were left — one 

 control, which was normal, and two of the treated plants, which were now 

 forming tubers with extreme rapidity, and from which the "artificial" rolling of 

 the leaves had almost disappeared. Two days later the leaves of the then only 

 remaining treated plant had entirely lost their rolled appearance (see figs. 4 



^It should be stated that during the period of the experiment primai-y leaf-roll had 

 become common in neighbouring healthy plants in the same plot. All these plants were much 

 infested with capsid bugs (Calocoris hipiinctatns), which came from an adjacent weedy- 

 hedge, and infection was attributed to them. 



