150 NOTES AND MEMORANDA. 



the root in all the important groups of Phanerogams.* The results of 

 his investigations show that the characters of the apex of the root cannot 

 serve for the appreciation of the reciprocal relations of the families, 

 and that the views of M. Treub on the taxinomic importance of these 

 characters are not well founded. Plants most closely allied often 

 differ very much in the structure of the apex of their roots, and on 

 the other hand, plants belonging to widely separated families have 

 common radicular characters. 



The structure of the vegetative summit can in fact only serve as 

 regards classification to establish positively whether a plant is a 

 monocotyledon or a dicotyledon. 



Removal of Air from Microscopic Specimens.— Much difficulty 

 has been experienced by the working microscopist in removing air 

 from his specimens, especially with wood sections, and various 

 methods have been adopted with greater or less success. One method 

 has been to soak the specimens, after they have been cut, in different 

 fluids for some length of time, such as turpentine, oil of cloves, and 

 the like ; these, however, give very unsatisfactory results, sections of 

 wood having lain in oil of cloves for over three years without the air- 

 bubbles having been all removed. Eecourse has also been had 

 ineffectually to the air-pump, and microscopists have been at their 

 wits' end to discover some process by which their object can be 

 perfectly and satisfactorily accomplished. 



It is claimed t for Dr. Johnson, of Providence, E.I. (U.S.), that he 

 has discovered an effective method. The apparatus he employs is of 

 very simple construction, being a digester, or a common dentist's 

 vulcanizer, the means — steam. The specimens to be thus treated, 

 especially those of wood, are prepared in the usual way, and made 

 ready for mounting. They are nest placed in a small vessel of any 

 material which will resist a certain amount of heat. Dr. Johnson uses 

 a small glass phial in his experiments ; this is filled up with water 

 after all the specimens, as many as it can conveniently hold, are 

 placed within. A cork can be used, but a slit must be cut in it to 

 allow the escape of air and the admission of steam and hot water. 

 A little water is now poured into the vulcanizer, the bottle of objects 

 placed within, and the lid of the machine screwed air-tight. The 

 whole is then heated to a temperature of about 300° Fahr. for a few 

 minutes. This temperature is sufficient for all practical purposes ; a 

 higher degree of heat is unnecessary, or a longer time to remain at the 

 given temperature needless. 



When sufficiently cooled the phial is removed, the water drained 

 from the bottle, and alcohol substituted. The specimens are now 

 ready for mounting, or can be bottled and set away indefinitely for 

 use. 



This constitutes the whole process; by it the specimens are 

 absolutely free from air. Perfect satisfaction is guaranteed ; and in 

 every case we are absolutely sure of the results, provided, of course, 

 that the proper care has been taken. 



* 'Ann. Sci. Nat.' (Bot.), Gth ser., vol. vi. (1878). 

 t 'American Naturaliat,' vol. xiii. (1879) p. 57. 



