242 GROWTH 



diminishes gradually until it ceases altogether when the part is 

 mature. The time occupied by this gradual rise and fall is 

 termed the grand period of growth. 



It is also noticed that the vigour or energy of growth of a stem 

 or other member varies during the grand period : at one stage 

 of the development of the complete stem the growing part either 

 grows more rapidly or continues its growth longer than at 

 another stage. For example, during the youngest stages of the 

 development of most stems the energy of growth is low and 

 short internodes are produced, later the energy increases, and 

 larger internodes arise, afterwards the length of the internodes 

 diminishes in consequence of a gradually decreasing energy 

 of growth. 



Ex. 141. — In autumn before the leaves have fallen, cut off branches from 

 the common trees and shrubs, and measure the length between the several 

 internodes on that part of each branch which has grown during the same 

 season. 



Note the general rise and fall in the length of the internodes. 



Note also the relative size of the leaves at each node. 



Make similar measurements on the stems of annual herbaceous plants. 



Ex. 142. ^Repeat experiments 15 and 20: similarly mark with Indian 

 ink at intervals of A inch the second and third leaves of a young onion plant 

 soon after they appear; measure the intervals after the leaves have con- 

 siderably lengthened, and compare the growth with that of a bean root. 

 Is the region of greatest growth near the end of the leaf? 



Ex. 143. — Select a stem of wheat or barley in which the ear is just ap- 

 pearing ; cut about half-an-inch below the first and also below the second 

 visible node from the top, so as to obtain about one internode of the stem. 



Remove the leaf-blade and a small portion of the leaf-sheath and care- 

 fully measure the total length of the stem and the small part of it below 

 the node. Make five or six marks with Indian ink \ of an inch apart at 

 the upper part of the stem. Then place the lower end of the stem in 

 water, cover the whole if possible with a glass globe and leave it in a warm 

 room for twenty-four hours ; or place the stem in a glass cylinder with a 

 little water at the bottom for a similar period. 



Measure again the total length ; how much has the stem grown, and has 

 the growth taken place near its upper marked end or near the base ? Has 

 the small portion below the node grown at all ? 



Ex. 144.— Measure the length of the internodes on a few shoots of any 



