Further Growth and Duration of Plants ' 33 



boom), and Rhus lucida, Linn. (Taai bosch), are being destroyed 

 to obtain this substance. 



In summer there are rifts in the bark which admit air and 

 also 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 

 (Melia Azedarach, L.) they extend horizontally, and in Ery- 

 thrina they are vertical. They become very conspicuous in 

 poplars as the trunk grows, and give the peculiar marking 

 to the bark. 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. 1 Mingled with the 

 northern trees all through South Africa are trees from Australia. 

 Do you know any ? Do they shed their leaves so that they 

 are quite bare at some time of the year ? Can you tell how 

 long leaves remain on any evergreen tree ? 



While roots are absorbing food material, leaves are taking 

 in air. In the green cells of the leaves water, with the dissolved 

 earthy matter, is combined with the carbonic acid gas obtained 

 from the air to form the food of the plant. 



Air, earth, and water seem at first rather unsustaining diet, 

 but when we consider, we find that people, in common with 

 other animals, since they depend altogether upon plants for 

 food, are nourished by the same materials. 



Leaf Fall. Toward the end of the season when the work 

 of the leaf is nearly finished, preparation begins for cutting it off. 



1 Chestnuts have not changed their time of flowering, so it is too cold 

 for them to bear fruit in the Orange Free State although they come from 

 a much colder country. 



