Murphy — On ihe Cause of Rolling in Potato Foliage. 



169 



and 5, PI. VI)/ and when removed from the plant on this daj' and subsequently 

 tested at intervals they were fovind to lose their starch fully as quickly as 

 corresponding leaves from an untreated healthy control plant of the same 

 variety (see fig. 8, PI. VI), as the following details will show : — 



It appears that Voehting (1.5) long ago carried out a somewhat similar 

 experiment, but not, of course, with reference to leaf -roll, and no mention seems 

 to have been made of any resulting change in the form of the leaves, although it 

 is apparent from some of the figures that a certain amount of rolling set in. 

 That it was not more pronounced is probably due to the formation of aerial 

 tubers, which provided an outlet for the large amount of starch that accumulated. 

 Quanjer et al. (11) also refer to the presence of excess of starch in the stems 

 and leaves of plants from which the tubers have been removed, and in those the 

 stolons of which are attacked by Coriicium vagum ; but no reference is made to 

 any rolling of the leaves following these occurrences. 



Prom the results of the experiments described in this and in the preceding 

 sections of this paper it is concluded that one of the earliest discernible effects 

 of the leaf-roll disease is an abnormal accumulation of starch, principally in the 

 lower leaves of affected plants. It has been shown that the starch disappears 

 at the normal rate from these leaves at first. At a somewhat later period, there 

 is a gradual retardation of this process, and, following rapidly on this, the 

 leaflets begin to roll upwards at their margins. Seeing that in the case of 

 affected plants rolling appears to follow starch accumulation, and that the rolling 

 of the leaves of diseased plants can he prevented for comparatively long periods 

 by the exclusion of light, and by thus greatly reducing the amount of carbon 

 assimilation ; and further, in view of the fact that rolling and starch accumula- 

 tion can be induced in healthy plants when they are deprived of their storage 

 organs and most of their growing points— there is little room for doubt but that 

 the rolling of the leaves of diseased plants is a direct consequence of the accumu- 

 lation in them of an excess of starch." 



Distention of the spongy 2'>ci.renchyma. — This accumulation of carbohydrate 

 in the tissues of affected leaves leads to an abnormal distention of the spongy 

 as compared with the palisade parenchyma. Owing to the fact that the spongy 

 parenchyma is comparatively free to expand in three directions, but is restricted 



' An unusual feature of some of the treated plants may be noted in fig. 4— namely, the 

 prolongation of the Tiltimate branches of the floral shoot into shoots which bore small foliage 

 leaves and developed new flower buds at their tips. The floral axes on these plants were un- 

 usually stout and well developed, and in one case fruit was set, which is a very rare occui- 

 renee in the case of Up-to-Date. These phenomena are no doubt related to the presence ot 

 an abnormal amount of food materials in the upper portion of the treated plants. 



= It is quite probable, as appears from Neger 's work, that an abnormal amount ot sugar 

 is also present in rolled diseased leaves. This point was not investigated. 



