130 The Irish Naturalist. March, 



species flowered for the first time in cultivation at Glasnevin. It belongs 

 to the section in which the labellum has a well-marked marginal fringe 

 of hairs. In the species under consideration the hairs are long, white, 

 and very fine. The labellum is so delicately balanced that the slightest 

 movement of the air which catches the long hair, causes it to vibrate 

 rapidly. 



Dr. Francis A. Winder showed the larval form of a scarlet earth 

 mite {Trombidium sp ) that is known as the "Harvest-bug," or "Orange 

 tawny," Leptits autumnalis. In this stage the mite has 011I3 7 six of the 

 eight legs that characterise the adult, and its habit of burrowing into 

 the skin of persons who have been among the vegetation whereon the 

 mites breed is well known, as its presence on the human body sets up 

 an intolerable irritation. These larvae are found also on various 

 domestic animals, and on wild mammals. Only in the larval stage are 

 these mites parasitic ; the adults feed by suction from plant tissues. 



Dr. G H. Pethybridge exhibited sections of a leaf of a plum tree 

 suffering from the disease known as " Silver-leaf." The silverinessofthe 

 leaf is due to the death of the upper epidermis and its separation from 

 the underlying cells, the spaces thus produced becoming filled with air. 

 In some cases the epidermis had entirely disappeared, and the cells of 

 the uppermost layer of palisade parenchyma were also dead Not the 

 slightest traces of any fungus can be found in these silvery leaves. The 

 cause of the disease has long been a mystery, but Percival seems to have 

 proved that it is due to the roots and stems being attacked by Stereum 

 pitrpweitm. A specimen of this fungus was exhibited growing on the 

 branches of a plum tree, but not from the same tree as that from which the 

 silvery leaves exhibited were derived. The fungus was sent by a horti- 

 culturist in Co Down as being the cause of the death of the plum tree, 

 but unfortunately too late in the season to admit of any leaves of this 

 tree being examined, since they had all fallen. Writing from memory 

 the sender says "the general appearance of the leaves was delicate and 

 pale as if attacked with mildew, but on close examination there was 

 no mildew." Probably these were *• silver-leaves" (although the sender 

 himself does not think so), and this case would tend to support Percival' s 

 explanation of the cause of the disease. 



W. F. Gunn showed the leaves of culinary Peas suffering from a 

 mildew, Erysipht Martii, Lev. which was very prevalent in some parts of 

 the country last summer. The microscope showed the leaves crowded 

 with minute black perithecia embedded in the mycelium of the fungus. 

 The disease, though not very deadly, spoils the appearance of the plants, 

 and diminishes the crop. 



January 9. — The Club met atLeinster House. 



Dr. G. H. Pethybridge (Vice-President) in the chair, exhibited the 

 fungus causing the American gooseberry mildew (Sph&rotheca mors-uva) in 

 its winter or resting condition. On the gooseberry twigs amongst the 

 brownish surface mycelium, the black perithecia, just visible to the 

 naked eye, are to be found in large numbers. On applying gentle 



