102 Mr. W. Gardiner. The Histology of the Cell Wall, 



appears generally necessary to bring about a definite swelling of the 

 cell wall. Thirdly, that it is not easy to stain and isolate the threads, 

 even when they are known to be present. 



These facts place many obstacles in the way of successful research. 

 The difficulties attending the manipulation of fresh tissue are 

 sufficiently obvious, and are apt to be so increased by the subsequent 

 swelling as to render any really refined investigation well-nigh 

 impossible, and as long as the threads cannot be stnined so as to 

 stand out clearly from the rest of the wall their identifi cation is out 

 of the question. These difficulties, which are sufficiently pronounced 

 in the case of peculiarly favourable material such as that of endo- 

 sperm, are only magnified when the investigation is concerned with 

 ordinary or young tissue. In addition to the drawbacks already 

 mentioned, the existing methods of research hitherto in use make 

 no provision for the preservation of tissue. 



It became obvious, therefore, that if the inquiry into the relations 

 of the cell wall and the connecting threads was to be prosecuted 

 with success, a more refined method must be devised, which could 

 be reduced to terms of the usual procedure, viz., killing, fixing, 

 hardening, preserving, cutting section, staining, and mounting, and 

 that the methods heretofore in use were too coarse for so delicate an 

 investigation. 



I do not propose in the present paper either to give an account 

 of the discovery of my method, or to go into elaborate technical 

 details. It is sufficient to say that, expressed in the simplest 

 terms, the method appears to depend upon the use of two prin- 

 cipal reagents, viz., the osmic-acid-uranium-nitrate mixture of 

 Kolossow- as a fixative, and safranin as a dye. As a preservative I 

 have used thymol water, and have obtained excelleut results with 

 material which has remained in it for as long a period as three years. 

 Sections may be cut by hand or with the freezing microtome. 



The fixing and staining reagents must be introduced and employed 

 in different ways, the exact manner of procedure depending upon 

 the character and age of the particular tissue under observation. 

 This can be best illustrated by means of definite examples, and since 

 the whole method is somewhat complicated, it will be expedient to 

 consider under separate heads (1) the killing and fixing, with which 

 is also associated the swelling, and (2) the staining. 



In material such as that of young endosperms (e.g., the endosperm' 

 of Tamus communis), no swelling is required, and the tissue, cut 

 into small pieces, may be both killed and fixed at one and the same 

 time by Kolossow's reagent, and then preserved in thymol water for 

 future use. Where cnly slight swelling is necessary, treatment with 

 water may precede that of Kolossow's reagent. In certain classes of 

 tissue, where the walls are swollen with comparative ease, such as 



