44 



METHODS IN PLANT HISTOLOGY 



largely upon the Griibler products. In general, it would seem that the 

 American stains are purer and that they act more rapidly. 



The current practice in staining paraffin sections on the slide differs 

 from the practice in staining freehand sections or small objects which 

 are to be mounted whole. In case of paraffin sections, the cell contents 

 are usually as important and often more important than the cell walls; 

 consecjuently, extreme care must be given to every detail. With free- 

 hand sections the cell contents often drop out, but even when they re- 

 main, the cell walls are usually the important features; and so the 

 process is considerably shortened. 



For staining freehand sections, it is customary to use solid watch 

 glasses, unless the sections are very large. The details of the method 

 are given in chapter vi, on "Freehand Sections." 



Fig. 16. — Arrangement of staining-dishes 



For staining sections on the slide, nothing is better than the ordi- 

 nary Stender dish. The arrangement of Stender dishes shown in 

 Figure 16 is very convenient. The advantage is obvious. With two 

 dishes each of xylol, xylol-alcohol, absolute alcohol, and 95 per cent 

 alcohol, one set can be used in passing down to the stain, and the other, 

 which is thus kept free from any paraffin in solution, can be used 

 in passing back to the balsam. Even for paraffin sections, some use 

 only three alcohols, 50, 95, and 100 per cent, and the first two may be 

 simply poured over the slide; in this case, only one Stender dish — for 

 the 100 per cent alcohol — is necessary in the alcohol series, the other 

 two alcohols being kept in bottles. This short method gained great 

 popularity because it was used in Strasburger's laboratory at Bonn. 

 It was the influence of this school and its great master which led to 

 the adoption of the short schedule in the second edition of this book. 

 A few years' trial showed the weakness of the method, and we re- 

 turned to the longer schedule. The crudeness of the short schedule is 

 doubtless responsible for the tenacity with which the Bonn school has 

 clung to the theory of linin and chromomeres. The young investigator 



