OF THE GREEN CELLS OF PLANTS 61 



So far as we have been able to discover there exist no records later 

 than the above in the literature of the subject on the occurrence of 

 iron in the chloroplasts of the green cell, nor any information as to 

 the form in which iron compounds are present. No investigations 

 with the iron haematoxylin test of Macallum appear to have been 

 made hitherto upon plants. 



EXPERIMENTAL METHODS. 



In carrying out tests for the detection of inorganic iron in the 

 chloroplasts, and in plant tissues generally, two points must be 

 carefully borne in mind : first, the previous preparation of the tissue 

 and its subdivision so that the parts possibly containing iron may be 

 penetrated by the reagents used for the detection; and secondly, 

 that the reagents be applied carefully so that false results are not 

 obtained. Here care must be taken with the concentration of the 

 reagents and the relative periods of time within which positive 

 results are obtained. 



In regard to the preparation of the tissues, if sections are to be 

 cut, care must be taken that this is done with a clean burnished 

 knife. Control experiments show that a clean steel knife leaves no 

 iron on the section. But, in most cases, since the question at issue 

 is not the structural arrangement but rather whether this or that 

 constituent contains iron, it is better to work with finely teased or 

 broken-up tissues. For this purpose glass rods drawn out to a 

 point were always used instead of steel needles, and also, in order to 

 break up some of the green cells and set free the chloroplasts, a 

 portion of the tissue in each case was still more broken up by turning 

 upon it the blunt end of the glass rod and grinding it between this 

 and the microscope slide on which it was being mounted. 



In choosing tissues for examination, preference so far as possible 

 is given to those where the chloroplasts are more conspicuous in 

 size, and also in some cases, such as spirogyra, delicate filaments 

 were chosen which could, after extraction as described below with 

 alcohol, be mounted without breaking up. 



In certain cases, such as pleurococcus, staining can readily be 

 obtained without previous chemical preparation of the tissue, but, 

 in the majority of cases, the lipoids present along with the chloro- 

 phyll in the chloroplast prevent the penetration of the stain, also 

 the green colour modifies and masks the blue of the haBmatoxylin in 



