and Laboratory Methods. 1529 



meristem can be shown in all growing tubercles. In sufficiently young and 

 recently infected roots, the course of the infection threads from the root-hairs to 

 the pericycle can be clearly demonstrated. 



The success in embedding, sectioning, and staining root-tubercles which 

 follows the application of the methods just described, makes it difficult to under- 

 stand the difficulties which prompted Miss Dawson ^ to declare " the tubercle 

 tissues very difficult objects to stain upon the slide," and that "ordinarily thin 

 hand-sections serve better for the examination of the filaments within the cells." 

 Miss Dawson used with success the following method, but it lacks some of the 

 advantages possessed by the one I have used. She placed " sections hardened in 

 alcohol (best without previous treatment with chromic or osmic acid) " " for about 

 two hours in alcoholic potash (one part 5 per cent, potash to three parts absolute 

 alcohol) and then passed into Eau de Javelle for ten minutes. From this solution 

 they are transferred to the dye, which is prepared by mixing an alcoholic solution 

 of anilin blue with orseillin, drop by drop, until a violet solution is obtained. 

 This mixture is acidulated with a few drops of glacial acetic acid. The sections 

 remain in the stain for two hours, and are then transferred directly to dilute 

 glycerine, and finally mounted in glycerine." This method of Miss Dawson's is 

 merely an improvement in definiteness of statement of the one described by 

 Strasburger in his " Praktikum." One of the stains which she used, Orseillin, 

 is not obtainable under that name in this country, and I do not know whether 

 she means Orcein or Orseille, two stains made by Griibler and carried in stock 

 here. 



However, it is not my intention to criticise Miss Dawson's method or her 

 description of it, but rather merely to describe my own, which anyone sufficiently 

 interested to try it will find practicable. 

 Leland Stanford Jr. University. " George J. Peirce. 



MICRO-CHEMICAL ANALYSIS. 

 XVIII. 



In order to be consistent with a former statement we should properly con- 

 sider in this article the analytical reactions of the element mercury ; this element 

 falling in the same group in the periodic system as the elements last considered. 

 Unfortunately there is still a missing element between cadmium and mercury, 

 thus causing a serious break in the series. The change in chemical behavior 

 which we find, in passing from cadmium to mercury, is such that so far as our 

 micro-chemical tests are concerned, there are practically no analogous reactions 

 existing between mercury and the other members of the group. 



On the other hand, so many of the properties of aluminum, the horizontal 

 analogue of magnesium, are closely related to those of the group last discussed, 

 that it has been thought best to take up aluminum at this point. Moreover, we 



2 Dawson, Maria. Nitrogin and the Nodules of Leguminous Plants. Philos. Trans. Royal 

 Soc, London, 1899. 



