224 Studies in ludian Cotton 



necessary receives recognition in the use of the word " typical." Tiiese 

 precautions require examination since, in a purely arbitrary deter- 

 mination of this nature, some control is required to ensui-e that the 

 restrictions imposed by their use are not of a nature to render valueless 

 the figures so obtained. Such a check has been found in the measure- 

 ment of the leaves of one individual of each of the several pure 

 types isolated, only the earliest leaves of the main stem and the 

 diminutive leaves at the base of each branch being excluded. These 

 measurements were made at intervals of about a week throughout 

 the season, each leaf being thus measured as it became fully expanded. 

 The results of one such determination in the case of a plant of type 5 

 are set out in Table IX. For the purpose of their undersUmding the 

 leaves may be grouped into four sets : 



(1) Leaves borne on the main stem. 



(2) „ „ monopodial secondary branches. 



(3) „ ,, tertiary branches. 



(4) ,, „ sympodial secondary branches. 



It will be noticed that the monopodial secondary branches alone 

 bear tertiary branches which arc almost invariably sympodial. The 

 values obtained for the average leaf factor of these four groups are 

 respectively : 



(1) 1-82, (2) rs-i, (3) 1-73, (4) 172. 



It will be noticed that the leaf factor of the leaves borne on the 

 monopodia is definitely larger than that of the leaves borne on the 

 sympodia whether these be secondary or tertiary branches. The value 

 of the leaf factor as determined for the leaves arising from the mono- 

 podia, differs by between 006 and 004 from the value obtained by 

 the empirical method of selection of " typical " leaves. This error lies 

 well within the limits of the experimental error as defined above. The 

 " typical " leaf, therefore, may be defined as that leaf which possesses a 

 factor having a value ecpial to the average of the factors of all leaves 

 arising from the monopodial branches. It is not, as was anticipated 

 when the author's earliest note (11) was pulilished, the average of th 

 factors of all the fully developed leaves. 'J'liis result is in perfect accord 

 with the main precaution which on empirical grounds it has been found 

 advisable to take, namely, to select leaves from the monopodia. It is 

 these leaves that the eye naturally selects as being typical of the plant. 

 It is perhaps unnecessary to detail more than one further precaution 

 which it has been found advisable to adopt. This is to avoid the 



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