8o The Irish Naturalist. March, 



markings were most irregular in shape and size, and confined 

 to the upper surface of the leaves. But, what was quite 

 unusual, the markings were not flat, but appeared as prominent 

 blisters rising more or less above the general surface of the 

 leaf, according as the markings were larger or smaller. Closer 

 examination of these prominences showed that they were 

 only pseudo-blisters, that is to say, they were not caused by an 

 internal expansion of the leaf-tissue, but by a protrusion of the 

 entire leaf substance, the prominence on the upper .surface 

 corresponding in every case most accurately with a depression 

 on the under surface. The leaves were, in fact, rcpoiissees, to 

 borrow an expressive term from the arts. The contour of each 

 pseudo-blister coincided exactly with the highly irregular 

 outline of each blotch on the leaf, and every leaf aflfected had 

 every one of its blotches, from the smallest to the largest, 

 equally defined by a prominence above and au answering 

 depression below. No such pseudo-blisters appeared any- 

 where on the green or unblotched parts of the affected leaves. 

 Only some of the maculate plants developed these blisters. 

 Others, a short way distant from the affected plants^ showed 

 not the faintest trace of protuberance on the surface of their 

 blotched leaves. 



The aspect of these curious leaf-swellings at once suggested 

 a morbid condition, arising, perhaps, from the attack of au 

 insect or fungus. But no trace of either could be made out 

 when the blotches \\ere examined under a quarter-inch ob- 

 jective. Fresh specimens submitted to Mr. Greenwood Pim 

 and to Mr. G. H. Carpenter were returned to me with a re- 

 port from the former that he could find no fungoid growth, 

 and from the latter that he saw nothing to suggest the attack 

 of an insect. 



The cause of the pseudo-blisters on the Arum leaf would 

 appear then to be a mystery still awaiting solution, and the 

 present writer can only throw out as a suggestion for future 

 inquiry the following hj^pothesis. It is briefly this — that the 

 leaf-swellings are the effect of the sun*s heat acting unequally 

 on the surface of the blotched leaves, the dark parts absorbing 

 this heat much more actively than the green, so that the 

 tender leaf substance is subjected to a system of strains which 

 results in apparent blisters placed precisely in the region of 



