CHAPTER XIV. 



TWIGS. 



Definition Winter twigs Tegumentary layers Surface characters 



The colours of twigs. 



In the narrower sense of the word, as here employed, 

 a twig is the shoot which has passed through its period 

 of growth in length, and on which no new leaves or other 

 structures appear in the ordinary course of events i.e. apart 

 from anything of an adventitious or abnormal character 

 which may be formed owing to injuries or other stimuli. 

 Confining our attention principally to our deciduous trees, 

 the twig in its winter state usually exhibits the following 

 peculiarities. 



Its epidermis, except in a few rare cases where that 

 layer is capable of living for many years as in the 

 Mistletoe, is being replaced or has already been replaced 

 by corky tissues, or periderm, the pressure of which 

 causes the former to split or flake off, and changes 

 the previously green colour of the shoot to some other 

 colour. That green colour was due to the hue of the 

 chlorophyll in the cells of the cortex shining through the 

 thin semi-transparent single layer of the epidermis: the 

 tint generally greyish to olive or brownish which 

 predominates as the periderm develops, is due partly to 



