182 



Journal of Agricultural Research 



Vol. XX, No. 3 



Palladin (14) also found that the composition of the normal green and 

 etiolated specimens of Vicia faba, the latter having been grown in the 

 absence of light, differed in composition in the same general way as the 

 normal and albino plants reported by Church. Weber (16) studied the 

 effects of different parts of the spectrum on the composition of plants 

 and found similar effects. Jensen (7) has recorded similar observations 

 on the leaves of the privet plant, Ligustrum aurea. 



While the fundamental cause of vegetable albinism is not known, 

 the fact that light of certain wave lengths is essential to the formation of 

 chlorophyl is well known; but in mottled citrus leaves the deficiency 

 of chlorophyl certainly can not be caused by an insufficiency of light. 



The fact that the composition of albino and etiolated plants differs 

 from that of normal specimens in the same general way as is the case 

 with mottled and normal citrus leaves shows that different causes 

 may bring about similar effects in different species of plants. This fact 

 also suggests at once that the composition of a plant may not afford a 

 safe basis for forming a judgment as to the cause of a particular phenom- 

 enon. A satisfactory elucidation of these questions is not possible at 

 present owing, in part at least, to the lack of definite knowledge con- 

 cerning the fundamental principles underlying the growth processes of 

 plants. The formation of chlorophyl is undoubtedly the result of a 

 number of interdependent factors, and it is highly probable that either 

 the absence or the inhibition of any one of these factors may prevent the 

 formation of chlorophyl or ultimately lead to its decomposition. 



COMPOSITION OF THE SAP OF ORANGE LEAVES 

 Some study has also been devoted to the sap of orange leaves. The 

 sap was obtained by first subjecting the leaves to a temperature a few 

 degrees centigrade below zero for a period of several hours. Im- 

 mediately after the leaves were removed from the freezing chamber 

 they were quickly ground to a pulp with an ordinary meat grinder. 

 The juice was then pressed from the pulp by the use of a hand-screw 

 press. A portion of the juice was filtered through folded filter paper, 

 and its specific gravity was determined by the pycnometer. Partial 

 analysis was made on weighed portions of the juice by first evaporating 

 to dryness and then using the methods previously described. Special 

 investigations were also made on unfiltered portions of the sap as described 

 below. 



Mature normal leaves, collected from healthy navel orange trees on 

 May 29, 1 91 8, were first studied. A sample of 861 gm. of leaves yielded 

 approximately 1 50 cc. of sap. Partial analysis gave the following results : 



