GENERAL CHARACTERISTICS OF GROWTH 



325 



most favorable of environments. A bacillus may be a micron in 

 diameter, and a redwood (Sequoia) may reach the height of over 

 300 feet. The eucalyptus trees of Australia are even taller than 

 the redwoods, but their diameter and total bulk is much less. 

 Some of the kelps among the brown algae may reach a length of 

 600 feet. This shows the great variation in size among the mem- 



Fig. 22. — Diagram of Lonicera leaf showing region of growth. A is a leaf 

 immediately after it is marked and B the same leaf after two days. Note 

 that all parts of the leaf have grown, but the base and apex have grown 

 slightly more than the rest. 



bers of the plant kingdom, — differences which are not related to 

 nutrition, light, etc., but are inborn and connected with the past 

 history of the species by bonds so tight that nothing man can do 

 will break them. 



A third internal factor closely connected with the externaL 

 water supply is the turgidity of the cell. No cell will reach its 

 maximum size unless there is present enough water to maintain 

 the protoplast firmly pressed against the cell wall. This effect 

 of turgor may be a purely mechanical one but it is none the less 

 important. Unless there is abundant water, the cell will not 

 enlarge or grow. 



Periodicity of Growth.— In the temperate climates, growth 

 periods are closely associated with the external environment. In 

 spring when water, temperature, etc., are favorable, growth be- 

 gins. Later it reaches a maximum and then slows down in the 

 autumn with the shedding of the leaves, as the unfavorable condi- 

 tions of winter approach. That this periodicity is not purely 

 environmental, however, is shown by the fact that some plants 

 grown in the north and carried to a tropical country where growth 

 conditions are favorable the entire year, still continue to shed their 

 leaves and to retain their regular resting period. Thus the oak, 

 beech, apple, and pear when transported to the subtropical cli- 

 mate of Madeira or to the tropical climate of Ceylon continue to 



