252 Methods in Plant Histology 



Laricio in the vicinity of Chicago, but dates will be different for differ- 

 ent species and even for the same species in different regions; P. 

 Laricio, at Chicago, sheds pollen about the middle of June, but P. 

 maritima at Auckland, New Zealand, sheds its pollen about the 

 first of October. After a year's collecting in any region, there should 

 be no difficulty, since the dates do not vary much from year to year. 



The Vegetative Structures. --The stem, root, and leaf will be 

 treated separately. 



The stem. The vascular cylinder is an endarch siphonostele, a 

 type which, with few exceptions, is found throughout the living 

 gymnosperms. 



The young stem in its first year's growth is green and soft and is 

 easily cut in paraffin. The best time to collect material is soon after 

 the young shoot has emerged from the bud scales in the spring. With 

 a thin safety-razor blade, cut the stem transversely into pieces about 

 5mm. in length; fix in formalin alcohol, imbed in paraffin, and 

 stain in safranin and light green. Longitudinal sections of the buds 

 in winter or early spring condition are instructive for comparison 

 with longitudinal sections of the ovulate cone. Trim away most of 

 the bud scales and cut a slab from opposite sides, leaving a piece 

 2 or 3 mm. thick to be imbedded. The bud, and also selected pieces 

 of the young stem, will show the structure of the young leaf. Later 

 in the season, even the first year's shoot should be cut without 

 imbedding. The two- and three-year shoots and all older material 

 should be cut freehand, without imbedding, and, preferably, before 

 fixing. Such sections are transferred directly from the knife to 95 

 per cent alcohol. 



For the structure of the adult stem, select a clear board and, for 

 transverse sections, cut out pieces about 15 mm. long and 6 to 10 mm. 

 square; for longitudinal sections, use pieces about 10 mm. long, with 

 5 and 10 mm. for the other two faces. Cut from the face which will 

 give sections 5X10 mm. Orient carefully, so that the longitudinal 

 radial sections shall be exactly parallel with the rays, and the longi- 

 tudinal tangential sections exactly tangential to the rays. Leave the 

 sections in 95 per cent alcohol for 15 or 20 minutes before staining. 

 Stain for at least 24 hours in safranin, extract the stain until only a 



