Nov. i, 1920 Composition of Normal and Mottled Citrus Leaves 1 79 



Severely mottled lemon and grapefruit leaves have also been analyzed 

 (Tables XII and XIII). 



The results show that the composition of mottled lemon and grape- 

 fruit leaves is similar to that of mottled orange leaves. As was found 

 from the analysis of normal leaves, the composition of lemon leaves 

 closely resembles that of Valencia orange leaves, while the composition 

 of grapefruit leaves was found to be like that of Navel leaves. How- 

 ever, the different varieties and species do not vary greatly in com- 

 position. 



The fact that the composition of the leaves of one species of citrus is 

 affected in the same general way as that of other species is not surprising, 

 since their appearance when mottled is also similar. 



As is well known, it is rare that all the leaves on a given orange tree 

 are mottled. As a rule, those growing on the outer portions of the tree 

 are the most severely affected, as sometimes, although not invariably, 

 is the case with the leaves borne on the south and southeastern portion 

 of the trees. The leaves of severely affected trees, however, may be 

 mottled throughout the tree. Frequently the greater portion of the 

 leaves borne by the shoots of a given growth cycle may be mottled, while 

 those immediately preceding and following this cycle may be entirely 

 normal in appearance. It is interesting, therefore, to compare the com- 

 position of normal and mottled leaves from the same tree. 



With this end in view, samples of normal-appearing leaves were col- 

 lected from the same trees from which some of the previously discussed 

 samples of mottled leaves were drawn and on the same days. The 

 analyses are reported in Tables XIV and XV. 



The data are concordant with the previously reported analyses of 

 normal leaves (Tables I and II). The results suggest that the leaves of 

 different cycles of growth are mutually independent in composition and 

 that the peculiarities in the composition of mottled leaves are not due to 

 any special peculiarity of the tree upon which they have grown. A leaf 

 of normal appearance borne by an orange tree the major portion of 

 whose foliage is severely mottled, as were some of these samples, has 

 approximately the same composition as any other normal orange leaf. 



Some study has also been devoted to citrus trees affected by chlorosis 1 

 and injured by alkali, the results of which will be presented elsewhere. 



The composition of albino and etiolated plants is of interest in this 

 connection. Church (4, 5) analyzed the normally green and albino por- 

 tions of the maple (Acer negundo), holly {Ilex aquifolium) , ivy (Hedera 

 helix), and several other species. He found that the albino portions 

 uniformly contained greater amounts of water than the green portions. 

 The ash of the former contained greater amounts of potash and phos- 

 phoric acid and lesser amounts of lime than the latter, while the content 

 of iron was approximately the same. 



1 Chlorosis of citrus, as it occurs in California, is distinguishable from mottle-leaf by a general fading of 

 the chlorophyl over the entire mesophyl tissue, while mottle-leaf, as the name implies, denotes the lack of 

 chlorophyl in spots between the veins. 



