GENERAL METHODS. 29 



the celloidin film. Therefore Overton dehydrates with 80 

 to 85 % alcohol and uses for the transfer to Canada balsam, 

 creosote, which will mix with even 70$ alcohol. From 

 the creosote the preparations are either placed directly in 

 Canada balsam or are passed first through xylol. Aniline 

 may be used for the same purpose by passing the objects 

 from 90$ alcohol to aniline, then to a mixture of equal 

 parts of aniline and xylol, and then to xylol (cf. 24). 



It should be noted also that many stains, as, e.g., Gentian 

 violet, stain the celloidin film strongly and are, therefore, 

 not to be used with this method. 



VIII. Microtome Technique. 



41. While the microtome has been generally used for 

 years by anatomists and zoologists, it has been used by 

 botanists in a comprehensive way only in recent years. 

 But since, so far as I know, no one who has recently taken 

 the trouble to familiarize himself with the technique of the 

 microtome, has denied the great value of microtome methods, 

 it seems superfluous to discuss here in detail their advantages 

 and disadvantages. 



I will only remark that the methods described in the fol- 

 lowing sections are not applicable to very hard objects, 

 especially to woods, while they have given me excellent re- 

 sults with all soft structures and also with most leaves and 

 herbaceous stems or roots. 



How far the methods proposed by Vinassa (I and II) for 

 cutting very hard objects, aided by a firmer microtome, 

 specially constructed for this purpose, are capable of general 

 application, I cannot judge for want of personal experience. 

 At all events it would be desirable, where possible, to so 

 modify Vinassa's methods as to preserve the protoplasmic 

 elements in the preliminary preparation of objects.* 



* [The Providence microtome, devised and sold by Rev. J. D. King, Cot- 

 tage City, Mass., is especially constructed for cutting hard objects and is said 

 to be well adapted to its purpose, but I am not able to speak from expe- 

 rience of it.] 



