Further Growth and Duration of Plants 31 



cork after different patterns. In blue gums the renewing cells 

 form long narrow plates, and the old tattered garment is shed 

 in long thin strips. In the oak and pine the pieces are small 

 and narrow but thick, while pieces of cork in the wild olive are 

 thin, small, and rough. Cork does not fall off as fast as it 

 cracks apart, but from a tree you can remove layer after layer 

 that has been formed in successive years. This portion of 

 the stem as far in as the cork is formed is known as the outer 

 bark. So long as the renewing cells, or cork meristem, are 

 not destroyed, cork may be removed without causing the death 

 of the tree, and so from the Cork Oak, bottle cork is removed 

 year after year. 



In this bark a substance called Tannin preserves the 

 wood from decay. Unfortunately for the tree, tannin is 

 excellent for preserving leather also, and so the beautiful 

 Protea cymar aides (Wagen boom), Le7Lcospcr7num conocarpoii 

 (Kreuple boom) and Rhiis Incida (Taai bosch) are destroyed 

 for this substance which w^as intended for their protection. 



In summer there are rifts in the bark to admit air and also 

 to allow escape of water. These can be seen on young stems 

 as small light-coloured raised openings. Being lens-shaped, 

 they are called lenticels. In Cassia and the Cape Lilac they 

 extend across the stem, and in Erythrina they are vertical. 

 They become very conspicuous in poplars as the trunk grows, 

 and give the peculiar marking to the bark. On quince bushes 

 they become large knotty growths. Lenticel cells are also 

 corky, but there are openings between them through which 

 water and air may pass. When trees take their winter rest, a 

 plate of cork seals them, so there is no waste of material. When 

 there is no income there must be no expenditure. In spring, 

 new spongy cells stretch and burst these little seals, and so the 

 lenticels can serve another season. Cork extends down to 

 cover the roots except the growing tip. 



Many of the trees introduced to this country from the 

 northern hemisphere are quite bare for a part of the year ; but 

 they have come to shed their leaves in July and August at the 

 time when they bear foliage in the north. Mingled with the 

 northern trees all through South Africa are trees from Australia. 



