SPERMATOPHYTES— GYMNOSPERMS 337 



The root. — The primary root should be studied in the embryo while 

 it is still contained in the seed. Collect material in September, October, 

 or at any later date. If material is collected in winter, the seeds should 

 be soaked in water for a day or two before fixing. In any case, remove 

 the testa and cut a thin slab from opposite sides of the endosperm to 

 facilitate fixing and infiltration. For secondary roots and also for the 

 structure of the stele in the primary root, germinate the seeds and fix 

 material after the hypocotyl has reached a length of 3 or 4 cm. The 



Fig. 117. — Picea nigra: photomicrograph of transverse section of root. Fixed in alcohol and 

 stained in safranin and Delafield's haeniatoxylin. Eastman Commercial Ortho film, Wratten B 

 filter (green) ; J. Swift and Son 1-inch objective; arc light; exposure, J second. Negative by Dr. P. J. 

 Sedgwick. X28. 



seeds of Pinus edulis, commonly called Pinon, or edible pine, can be 

 obtained in most cities. They are particularly good for a study of the 

 mature embryo and the seedling. 



The older roots are treated like the stems. The structure of roots 2 

 or 3 mm. in diameter is wonderfully regular (Fig. 117). 



The leaves. — Good sections of mature leaves of our common gym- 

 nosperms may be obtained in great quantities with little trouble by 

 the following method: Make a bunch of the needles as large as one's 

 little finger, wrap them firmly together with a string, allowing about 

 I inch of the bunch to project above the wrapping; dip 2 or 3 times 



