THE STEM. 169 



and Chenopodium albidum i i feet high have been 

 recorded. 



The annual increase in thickness varies greatly 

 according to the season and locality (see p. 317 et seq.). 

 The age to which trees may grow is often extraordinary, 

 but data regarding this are not easily gathered. Certain 

 Californian Redwoods are said to have been 3300 years 

 old, and European Cypresses and Yews are also said to 

 exceed 3000 years. It is obvious, however, that a 

 continuous existence in the same spot from B.C. iioo 

 to A.D. 1902, must be exceedingly improbable. It is 

 worth noting, that the more modern types of trees are 

 neither so tall, nor so longlived, as the ancient Sequoias 

 and other Conifers. In all other respects, the dicotyle- 

 donous Oaks, Beeches, etc., seem to be of a more 

 advanced type. The Spruce, the Douglas, Araucaria, etc., 

 show an exceedingly regular development of branches. 

 The leaves are invariably small, and though a young 

 thick-set plantation of Spruce forms a very dense and 

 complete shade, yet in older stages this shade is either 

 not maintained, or, only preserved by a continual dying 

 off of all the older branches. The branching, on the 

 other hand, of the ordinary dicotyledons, shows the 

 most exquisite adaptiveness to any unforeseen con- 

 ditions, and is never monotonous. 



Very little is known of the causes which produce the 

 various branch systems in deciduous trees. Of these there 

 are two distinct types : — those with opposite leaves, and 

 those in which the leaves are arranged alternately. The 

 branches of a Horse Chestnut may be taken as an example 

 of the first method ; the older branches begin next 

 the trunk with a slight ascending slope ; then they curve 

 gently over and descend towards the ground, which 

 they often nearly touch ; and, finally, they rise again 



