TRANSACTIONS OF THE SECTIONS. 133 



days in the case of branches kept in a room ; and I often had a drawing destroyed 

 by the accidental spilling of half a tea spoonfull of mucilaginous water on the 

 paper. The seed-pod when ripe is black; and I trust those now forwarded will 

 reach in sufficient safety to manifest the manner in which the seed with its silky 

 covering is packed up and afterwards dispersed. Each seed is about the size of a 

 small garden pea. It is, when in the pod, enveloped in a little cube of silk about 

 half an inch each way, slightly yellowish in the exterior. Liberated by the bursting 

 of the pod, when dry it flies out into the most beautiful smoke-like spirals and whorls 

 that can be imagined. Some few flowers generally remain on the tree till the bulk of 

 the seed-pods are ripe. The extraordinary beauty of the various portions of the seed- 

 pod of the Cochlospermtim Gossypium (of w r hich two varieties are sent) will be seen 

 from the specimens accompanying. 



Note on the Aversion of certain Trees and Plants to the Neighbourhood of 

 each other. By George Buist, LL.D., F.R.S. 



The accompanying drawings will afford some striking illustrations of the aversion 

 of certain plants to the vicinage of each other, not on the score of want of light, but 

 on that of want of air. I do not know that there is anything peculiar to our Indian 

 vegetation in this beyond what might be looked for from the heat of the sun and 

 the rapidity aud luxuriance of the vegetation. The first example is that of two 

 Casuarina trees eight years old, 40 feet in height, and 32 inches in girth, growing to 

 the right and left of the portico of my house. The house itself stands nearly north 

 and south ; the portico and much of the roof is covered with creeping plants. The 

 Casuarinas on each side bend away from this in nearly equal curves, one inclining to 

 the north, and the other to the south, receding 2 feet 8 inches at the height of 12 

 feet, so long as they are opposite to the other plants ; when above the roof of the 

 portico, they regain their perpendicularity immediately. 



The other case is that of young teak and a date palm, of no great size, and their 

 aversion to each other's neighbourhood is still more conspicuous. I have taken offsets 

 with a plumb and rule from each so as to give the precise amount of their retirement. 



A Diatomaceous Deposit found in the Island of Lewis. By H. Caunter. 



The deposit contained several species of Diatomaceae, and is situated in a lake-dis- 

 trict 1 50 feet above the level of the sea, and had evidently been deposited from a lake 

 now dry. It is situate in the western part of Uig, about five miles from the parish 

 church. 



An Account of the more remarkable Plants found in Braemar. 

 By Mr. Croall. 



Notes on the Upper Limits of Cultivation in Aberdeenshire. 

 By Professor Dickie, M.D. 



In a previous communication it has been shown that the three upper zones of 

 vegetation in Britain are well-represented in Aberdeenshire. Adopting as our 

 standard Mr. Watson's characteristics ('Cybele Britannica,' &c.) of the Agrarian 

 Region in Britain, we find that since certain species of indigenous plants, whose 

 presence marks the Infr-agrarian and Mid-agrarian Zones, are absent from Aber- 

 deenshire, as well as from the two neighbouring counties, and, I believe, from Scot- 

 land, the Supr-agrarian is the only one of the three which can apply to this district. 



The upper limit of Pteris aquilina (the common Brake Fern) is considered also 

 as marking the upper limit of the supr-agrarian zone, and therefore also that of cul- 

 tivation in Britain. The limit of this Fern in Aberdeenshire varies from 1600 

 to 1900 feet ; very rarely, however, does it attain the latter. In some localities, on 

 the bare stony sides of hills, I have found the limit to be 1600 to 1700 feet : even in 

 places where there is no cultivation, the common Mole makes its tunnels at about the 

 same height. On Morven I have seen it at 1723 feet ; and near Ballater, at Brakely, 

 it reaches 1642 ; at the Pulock Moss, 1735 ; and on the Khoil, 1800 feet. 



At various places, even more than forty miles from the sea-board, cultivation at 

 high altitudes is frequent ; farms at an elevation of one thousand feet are numerous, 



