132 FAMILIAR TREES 



huge trees of the same species in the "groves" of 

 California, which now rise bare of branches more 

 than 100 feet from the ground. 



The wood of the Coniferous stem is, as we saw 

 in our Introduction, very distinctive in its structure, 

 mainly by reason of its simplicity- as compared with 

 that of the broad-leaved trees. Though generally 

 quick-grown and soft, it is remarkable for strength 

 and durability. The stem increases in diameter 

 " exogenously," but its " cambium," or layer of grow- 

 ing tissue immediately below the bark, gives rise to 

 very uniform secondary wood, consisting of radial rows 

 ■of "tracheids" or elongated thick- waUed cells, divided 

 by pith-rays of only the width of a single cell, and in- 

 visible, therefore, to the naked eye. The " tracheids " 

 have on their radial walls numerous translucent thin 

 spots known as " bordered pits," which give a very 

 characteristic appearance to sections of Coniferous 

 wood under the microscope when they have been 

 cut " with the grain," i.e. longitudinally. In the stem 

 and in the leaves the Goniferce develop " ducts " or 

 tubular spaces in which the resin that constitutes 

 so marked a feature of the group is secreted. 



The leaves of Coniferce are simple and generally 

 evergreen, being either needle-shaped or at least 

 narrow, or flat and scale-like and closely adpressed to 

 the stem. The needle-like leaves have an internal 

 anatomy which is at once distinctive of each species 

 and specially adapted to restrict the amount of 

 transpiration. Their epidermis is made up of elon- 

 gated fibre-like cells, with very thick outer walls ; the 

 few stomata are deeply sunk among these cells ; the 



