230 NATURALISATION OF FOREST TREES. 



they can only be used as rough guides. For instance, trees with 

 broad soft horizontal leaves are obviously out of place in a dry 

 climate. Trees from dry mountain or desert regions with their 

 characteristic glaucous leaves, which reflect insolation and prevent 

 excessive temperatures in the leaves, are out of place in misty 

 climates, the dark green vegetation of which is adapted to absorb 

 all the available insolation. 



Influence of Scientific Naturalisation on the Form 



OF Forests. 



Before concluding, it may not be out of place to suggest the 

 influence which the scientific introduction of exotic trees must 

 have on the form of our plantations with regard to mixtures. 

 Whether or not mixed forests are desirable for other reasons, 

 it is obvious that where there are many local variations in habitat^ 

 there must usually be a corresponding number of suitable species. 

 This is perhaps particularly true of comparatively dry regions 

 in which slight changes in depth or nature of soil or in situation 

 make a considerable difference in the moisture conditions, but 

 it is also true of more humid regions. Almost all the forests of 

 the world consist of mixtures either of alternately pure stands, 

 or of mixed stands in which one species preponderates in one 

 locality and another in another. In forming mixed plantations 

 we are thus working in accordance with the laws of nature. 



Of course notable examples of pure forest exist in nature, such 

 as the pine forests of the plains of Prussia or the Landes of France 

 and it may be justifiable to reproduce these in aftorestation 

 here, but only where the same natural cause exists, that is uniformity 

 in factors of locality over a considerable area. 



The question of whether mixed stands of two species which 

 are both more or less suitable to the locality, are desirable, is 

 not in place here except that reference may be made to the fact 

 that it may often be desirable to make temporary mixtures with 

 nurse-trees and to the probability that many species which will 

 be failures in pure forest owing to their demands for shade and 

 relative humidity, will be successful as understories in permanent 

 mixtures, or at least may be sufficiently successful to play the 

 important role of undergrowth. 



In conclusion, I may say that the scientific study and practical 

 application of this branch of forestry in South Africa requires 

 centralisation and continuity of control as much as, if not more 

 than, any other branch, and it is only by the unification of the 

 various Forest Departments, that the best organisation for this 

 work will be rendered possible. 



PIDOUX'S COMET. —During- the latter half of February 

 another new comet was discovered by M. Pidoux at the Geneva 

 Observatory. The comet, which takes the designation 19 lo b, 

 occupied a position somewhat to the north of a point between 

 £ and c Piscium, Hallev's comet bein.tj at the time near to 

 the latter star, and less than ih degrees distant from the new 

 comet. 



