PTERIDOPHYTES— FILICALES 307 



tions 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, consequently, 

 the bud contains young leaves of three successive seasons. Two of 

 the three show a differentiation into sterile and fertile portions. 



YiG. 97. — Botrychium obliquum: photomicrograph of transverse section of rhizome. Fixed in 

 formalin-acetic-acid alcohol, and stained in safranin, gentian violet, orange. Paraffin section, 10 m- 

 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. 



In Osmunda, and in many other ferns of similar habit, the rhizome 

 is surrounded by the very hard leaf bases. Good sections of the central 

 cylinder can be secured only by dissecting away these hard leaf bases 

 and any hard portions of the cortex before attempting to cut sections. 

 A short distance back of the growing point will be found a region 

 which will show practically all the structures of the mature stem, 

 which will be easy to cut. Even in this region the leaf bases should be 

 dissected away. From the apical cell back to the region where the 

 sclerenchyma is beginning to turn brown, the material is easily cut in 

 paraffin. Older portions should be cut freehand. Osmunda affords an 

 excellent illustration of the mesarch siphonostele (Fig. 98). 



