DISTRIBUTION OF CONIFEROUS PLANTS. 37 



snow will permanently disfigure a tree whose branches have not 

 sufficient elasticity to yield to the weight without fracture. The 

 frondose branches of most Coniferse, with their dense clothing of 

 foliage, offer peculiar facilities for the resting of snow upon them, 

 and the weight of this, especially after being partially thawed and 

 then frozen, acts as a severe strain upon them. In the case of 

 young trees planted as specimens for the decoration of the lawn and 

 pleasure grounds, it is evidently advisable to relieve the branches of 

 at least a portion of their superincumbent weight after a heavy fall 

 of snow. The destruction of Coniferous trees by lightning is, at 

 least in this country, a rare occurrence. Whether this apparent 

 immunity is in any way owing to the resin contained in the wood 

 and sap, resin being one of the most perfect non-conductors of 

 electricity, does not appear to have been investigated. 



DISTRIBUTION. 



The distribution of the Coniferse over the globe, as j already 

 stated,* is general; the order being represented everywhere where 

 arborescent vegetation can exist, with two remarkable exceptions, 

 already pointed out.f The modifying phrase, " wherever arborescent 

 vegetation exists," is both necessary and important, for, besides the 

 Arctic and Antarctic Eegions where, under present conditions, no 

 trees grow, there are large tracts both in the Eastern and Western 

 Hemispheres that are treeless, the cause of which is, at least in 

 part, explained by the peculiar physical circumstances that influence 

 their climate. % The most extensive of these treeless regions in the 

 Eastern Hemisphere are (1)— The Steppes of South-Eastern Europe 

 and the great table-land of Central Asia which, together, stretch 

 across the continent from the River Don to the confines of China. 

 (2)— The Sahara Region, which, including the Arabian and Syrian 

 Deserts, extends from the Atlantic Ocean to the Persian Gulf. To 

 these may be added an extensive treeless tract in the interior of 

 Australia. In the Western Hemisphere there are (1)— The great 



* See page 5. 



t The Indian Peninsula and Central Africa. 



J They are not absolutely treeless, there are isolated spots and oases where springs of 

 water are found, and around which trees have sprung lip, Wit they are too few m number 

 to affect the general statement. 



