1 887-88.] Polarised Dark-ground lUumination. 1 27 



and many other most valued forms ; Soutli America, its arau- 

 caria; North America, a host of species of sorts which are 

 pecuhar to itself, including many which, we are persuaded 

 will rank one day as most useful timber-trees in Europe • while 

 Europe, including Great Britain, has its pines and spruces 

 which, while lending their own peculiar effects to tlie landscape' 

 are almost rivals to the oak as timber-producing trees 



From the very limited time at our disposal, and the magni- 

 tude of our subject, it seems very obvious that we will best 

 consult your convenience if we briefly allude to some of the 

 representative forms of the various genera on the table We 

 have arranged them in alphabetical order for easy reference • 

 the more scientific study of the various divisions must neces- 

 sarily be left for the private study of those who feel more 

 particularly interested in the subject. 



The following genera were then taken up seriaiim, and a short descrip- 

 .ve account given of the habit of growth, geographical distribution, and 

 cultivation 01 each : — 



Abies. 



Araucaria, 



Biota. 



Cedrus. 



Cephalotaxus. 



Chamsecyparis. 



Cryptonieria. 



Cupressus. 



Fitz-Roj'a. 



Juniperus. 



Larix. 



Libocedrus. 



Picea. 



Pinus. 



Prumnopitj's. 



Retinospora. 



Sciadopytis. 



Taxus. 



Thuja. 



Thujopsis. 



Wellingtonia. 



l\. —POLARISED DARK-GEOUND ILLUMINATION, 



Ey Mr WILLIAM PENMAN, Assoc. M.Inst.C.E. 



{Read Feb. 22, ISSS.) 



L.-VST session I had the honour of making a communication to 

 the Society upon the subject of "Diatoms under Dark-Ground 

 Illumination;" and as you have been good enough to embody 

 the paper m your 'Transactions,' I will not recapitulate the 

 methods and phenomena therein described, although thev 

 necessarily form the groundwork of the important subject I 

 now desire to bring before your notice 



