454 Dr David Chrisfcison on ascertaining 



2. In the two Acacias — mollissima and lophantha — which 

 were examined microscopically, true lines of demarcation, 

 although doubtful or invisible on the block, could be made 

 out by the naked eye in transparent sections, but sometimes 

 only with difficulty and after verification by the microscope. 

 Even under the microscope the line of demarcation was some- 

 times feebly marked, and the distinction between the autumn 

 wood on one side and the spring wood on the other was very 

 slight. 



3. In proportion to the shortness or imperfection of the 

 winter rest in the different species, the demarcation of the 

 zones appears to become less marked. Thus, in RoMnia, 

 which enjoys a long winter sleep, the demarcation of zones 

 is quite distinct on the blocks, and the minute structure of 

 the parts which contribute to the differentiation of the zones 

 differs but little from that of our British trees. But in the 

 Acacias, which have a short and, perhaps, in some seasons, 

 little or no rest, the demarcation of zones is often difficult, 

 doubtful, or even indistinguishable on the block, is seen with 

 difficulty by the naked eye in thin sections, and is compara- 

 tively feebly marked, in some instances, under the microscope. 



4. Quasi lines of demarcation, consisting of vessels arranged 

 in concentric circles, are met with in Melia and Bobinia. 

 They are easily distinguished, even by the naked eye, from 

 the true lines of demarcation, and do not form the limits of 

 zones differing in appearance or minute structure from each 

 other. In the Acacias there is a tendency to the same 

 concentric arrangement of the vessels, but they make no 

 show on the block, and the ringed appearance in these speci- 

 mens is perhaps mainly due to numerous concentric zones of 

 for the most part slightly-differing shades of colour. Under 

 the microscope these false rings are perhaps distinguishable, 

 but only by very trifling differences in the tissue indeed. 



It is interesting to note the variety in the duration of the 

 winter rest in the different species of trees measured by 

 Mr Hall, It is his intention to show this fully in a paper 

 upon the results of his tree measurements, to be read to our 

 Society in the present Session. In this place it is sufficient 

 to point out that trees introduced from England enjoy as 

 long a winter rest as at home ; that Melia azedarach, a native 

 of Syria and naturalised in the South of Europe, and Bdbi7iia 



