Triple-stained Section of Aristolochia 



223 





152 



Figs. 151 and 152. Details from an excellent preparation produced by the method 

 described in this example. Fig. 151 shows a general view of the stem. Notice at 1 

 that the lignified band is sharply defined and has remained attached to the outer 

 cortical cells. Fig. 152. Details of a vascular bundle. Notice at 2 the relatively unshrunk 

 cytoplasm showing a clear nucleus. The sharply denned wall of the vessel is shown 

 in 3, and 4 shows unshrunk well-stained phloem. 



portion of the stem should be cut into %-in. lengths with care so as to 

 avoid crushing, and the pieces washed overnight in running water. 



The process of dehydrating and clearing plant material is very different 

 from that used for animal tissues. Unless the greatest distortion of the 

 cell contents does not matter, it is necessary to employ the long series of 

 dehydrating mixtures given in Chapter 8, and it is recommended, at least 

 for the beginner, that he use two changes of tertiary butyl alcohol as the 

 last step. The tube containing the object in tertiary butyl alcohol now has 

 shredded into it about enough of the embedding medium to be used to 

 fill one-tenth of the tube. It is left in this condition overnight and then 

 about as much more wax added. This process is continued until there is 

 rather more wax in the tube than there was originally tertiary butyl 

 alcohol. It must be emphasized that this method of slow impregnation 

 is just as important for plant tissues as is slow dehydration and clearing. 

 The tube containing the sludgy mixture of wax and tertiary butyl alcohol 

 is now placed in the oven and left for 4 or 5 hr. The specimens are 

 then carefully removed to a container of pure molten wax. One hour 

 in this bath would be enough for a small section of stem. The piece is then 

 transferred to a second bath of pure paraffin for a further hour before 



