256 
METHODS IN PLANT HISTOLOGY 
metaxylem still being thin walled and staining with the light green. 
This rhizome affords an excellent illustration of a mesarch polystele. 
Dicksonia punctilobula has a small rhizome, often on the surface 
of the soil or rock, so that it is easy to get good clean pieces. About 
2 or 3 cm. back of the growing point, the xylem is well lignified, but 
the material still cuts well in paraffin. One could hardly find a 
better illustration of a mesarch amphiphloic siphonostele (Fig. 81). 
Fig. 82. —Botrychium obliquum: photomicrograph of transverse section of rhizome. Fixed 
in formalin-acetic acid-alcohol, and stained in safranin, gentian-violet, orange. Paraffin section, 
10 n. Eastman Commercial Ortho film, Wratten E filter (orange); arc light; J. Swift and Son 
1-inch lens; exposure, 1 second. Negative by Dr. P. J. Sedgwick. X45. 
Botrychium is widely distributed but individual plants are not 
abundant. The stem is erect, subterranean, and has an endarch 
siphonostele with secondary wood. Trim away the roots, which are 
very thick and fleshy in B. obliquum , fix in formalin-alcohol-acetic 
acid, and imbed in paraffin. Even the older parts of old stems can 
be cut in paraffin if you are sufficiently careful (Fig. 82.) Transverse 
sections from the base of the bud down to the secondary wood will 
give a beautiful series in the development of the stele. 
The bud at the top of this rhizome is an interesting object. The 
leaf is in its fourth year when it appears above ground, and, conse- 
