84 THE WHEAT PLANT 



The measurements indicate a wave of growth from the base to the 

 summit of the stem. The greatest increase occurred in the second 

 internode during the first two weeks, the greatest growth being transferred 

 to the third internode in the fourth and fifth weeks, to the fourth in the 

 next fortnight, to the fifth in the succeeding two weeks, and to the sixth 

 in the last fortnight, at the end of which no further addition was made 

 to the length of the stem or the ear. 



The figures in the vertical columns of Table II. also show that in each 

 internode and in the ear there is an acceleration to a maximum followed 

 by a gradual retardation in the rate of growth. 



The whole period of " shooting " occupied about eleven weeks, the 

 greatest increase in length both of stem and ear. occurring in the same week, 

 namely, May 23-30. 



At the time of its escape from the upper leaf-sheath in the week ending 

 June 6 the ear had almost reached its maximum length, being then only 

 i cm. shorter than the ear when full grown. 



The escape of the ear from the uppermost leaf-sheath marks a definite 

 and easily recognisable stage in the development of the wheat plant. 



The date at which it occurs is dependent upon a number of factors, 

 the chief of which are : 



1. The race, variety, or form of the wheat. 



2. The latitude and elevation of the place of growth. 



3. The rainfall, temperature, light, and general climatic conditions of 

 the season of growth. 



4. The date at which the seed is sown. 



Some Persian, Indian, Chinese, and Australian forms sown in 

 September or October at Reading come into " ear " at the end of the 

 following May, while many English wheats sown at the same time do not 

 reach this stage of development until the second or third week in June. 



The speed in attaining the " earing " stage, i.e. the " earliness " and 

 " lateness " of a variety, is a constant hereditary character which exhibits 

 the ordinary fluctuating variability, but is not permanently modified by 

 sowing the grain early or late or by varying the external conditions of 

 growth. Varieties preserve their characters in this respect no matter 

 where they are cultivated ; those which are relatively early or late in 

 India or Australia are early or late when grown in England, and rapid or 

 slow developing English forms exhibit the same relative differences when 

 transferred to another country. 



Schiibeler and others have asserted that a " late " wheat can be trans- 

 formed into an " early " one and vice versa by varying the date of sowing or 

 by transference to another climate for a time ; there is little doubt that a 

 mixture of sorts was sown in such cases and the conclusions were illusory. 



A " late " form is later in its ear production than an " early " form 



