V 



158 MISSOURI BOTANICAL GARDEN 



fixing fluid about 15 minutes and then washed in sea 

 water. The grades of alcohol used in dehydrating were 

 mixed with sea water. Sections were 



ma 



mi 



The first preparations were stained with Fleinmiug's 



safranin-gentian-violet-oransre stain. This stain did not 



o 



prove very satisfactory, as it overstained the cell walls. 

 Later in the work Haidenhain's iron-alum haematoxylin 

 method was used with good results. 



In the study of the apex both longitudinal and cross 

 sections were made and mounts were also prepared by 

 crushing in glycerin under the cover-glass. The growing 

 point of Mesorjloia divaricata so commonly turns to one 

 or the other side of the line of the axis of the stem, us to 

 making it a little difficult to get sections parallel to the 

 axis in this region. 



The apex of the stem consists of a central axial row of 

 cells terminating in an apical cell, surrounded by a sheath 

 of cortical cells except at its very tip (plate 38, f. 1). 



these cortical cells arise hairs and paraphyses, the 



44 Assimilationsfaden " of Kcinkc. Further from the tip 

 there may be two or more layers of cells in the cortical 

 sheath (figures 3, 4). In still older parts of the stem 

 there is a central cylinder consisting of the central row of 

 cells with two or more layers of thick-walled cells sur- 

 rounding it. As mentioned by Ilenckcl,* these are cells 

 that have been cortical cells in the younger stem. Bound- 

 ing the central cylinder near the apex is a zone of thin- 



m 



nd 



(figures 4, 5) 



The contents of the central cells soon begin to break 



down. 



ism 



S 



the cross-walls break down and the contents of the central 



Loc. cit. 



