ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 835 



The experiments were made upon the germinating maerospores and 

 the young embryos of Pilularia glohulifera, and the results obtained 

 warrant a very strong recommendation of the imbedding process where 

 the sectioning of very delicate tissues is necessary ; indeed, when the 

 results thus obtained are compared with the imperfect and uncertain 

 methods ordinarily used in such work, no one who has used both will 

 hesitate as to their comparative merits. With the firmer plant tissues 

 there is usually no necessity for any imbedding process, and owing to the 

 time and care necessary to successfully apply this method, it is not to be 

 recommended in such cases. 



In regard to the best hardening agents, Schonland and Moll disagree, 

 the former recommending alcohol, which Moll does not consider satis- 

 factory, preferring chromic acid or the mixture of chromic, osmic, and 

 acetic acids used by Flemming. There is no question that for many 

 purposes absolute alcohol is to be preferred, owing to its convenience 

 and the perfection with which it ordinarily preserves all plant tissues. 

 With mixtures of chromic, picric, or osmic acid thorough washing is neces- 

 sary after hardening ; but as Moll rightly remarks, where cuticularized 

 cell-walls are present it is extremely difficult to get the paraffin to 

 penetrate such membranes, whereas it is much easier where fixing solu- 

 tions containing chromic acid are employed. A practical illustration of 

 this was found in the very thick-walled maerospores of Pilularia. 



After the material is thoroughly hardened, and, in the case of alcoholic 

 material, allowed to remain for twenty-four hours in borax-carmine, it is 

 treated as described by Schonland. For the gradual transfer from 

 30 per cent, to absolute alcohol the Schultz apparatus * was found most 

 serviceable. 



The following method of imbedding was found practical and simple : 

 — A small paper box is made by taking a stidp of pretty firm paper and 

 winding it tightly about an ordinary cylindrical cork, fastening the paper 

 with a little gum arabic, and holding it in place with a pin until dry. 

 On taking out the pin the paper cylinder can of course be sli^Dped off the 

 cork. The box is completed by cutting out a round piece of paper of 

 exactly the size of the cylinder, and putting this into the cylinder as the 

 bottom of the box. The object to be imbedded is placed horizontally 

 upon the bottom, and the melted paraffin poured over it, after which the 

 whole is placed in a shallow flat-bottomed vessel filled with melted 

 paraffin. Thus there is no possibility of the paraffin's escaping, which 

 otherwise it is almost impossible to prevent, and there is also no neces- 

 sity of handling the objects after they are once in the paraffin, which in 

 the case of small objects is a great advantage. In case the objects are 

 displaced in pouring the paraffin over them, it is a simple matter to adjust 

 them, using a heated needle for this purpose. 



In order to insure thorough saturation, the objects were usually left 

 overnight in the melted paraffin, and then^ as in the articles mentioned, 

 quickly cooled to avoid the formation of bubbles. The vessel containing 

 the paper boxes may be exposed to the air for a few minutes until a thin 

 film has formed over the surface of the paraffin in the latter, when these 

 may be quickly lifted out and plunged into cold water. As soon as the 

 paraffin is thoroughly hard, the pasted seam in the paper cylinder may 

 be loosened with the blade of a knife or scalpel, when it will be found 



* Strasburger, Bot. Prak., 2nd ed. 



