222 



TEXTBOOK OF BOTANY 



result the growth of buds and the formation of new leaves 

 will become slower; and the plant, poorly supplied with 

 carbohydrate food because of its fewer leaves, will grow 

 weaker and finally die. Thus an erect or climbing plant 

 has a fairly definite limit of life, although the limit is very 

 different in different species. 



It is otherwise in plants with creeping or underground 

 stems. The older parts of these stems with the roots at- 



m^tm^. 



Fig. 134. — The base of one of the giant redwoods of CaUfornia. 

 Photograph by Squires. 



tached to them are constantly dying ; but the younger parts 



grow steadily forward, sending out new roots as they grow. 



So there seems to be no necessary limit to the life of plants 



such as these ; so far as we know, a plant with a creeping or 



underground stem might live indefinitely if the surrounding 



conditions remained favorable. Practically, the lives of 



most perennials are more or less shortened by injuries and 



by disease, and few if any reach the extreme age or the extreme 



size which would be possible if they remained perfectly healthy. 



240. The Largest and Oldest Plants. — The tallest known 



trees are the gum trees of Australia ; some of them reach a 



