THE SEED PLANTS 



683 



[Chap. L 



and two or three rows of sclerenchymatous cells beneath the epidermis 

 (Fig. 324). 



The stem of the pine is quite similar to a woody dicot (Chapter 

 XXVII) except for the absence of xylem vessels. The pine tree with 

 its leaves, branched stem, and root is the sporophyte. 



The sporophylls of the pine are spirally arranged in cones or strobili 

 (sing, strobihis). The cones are of two kinds: staminate and ovulate, 

 both occurring on the same plant (Fig. 325). 



Fig. 325. A branch of Austrian pine in June. At the tip of the youngest stem 

 segment are two small ovulate cones. At the tip of the next stem segment are two 

 one-year-old ovulate cones, and below them is a two-year-old ovulate cone. On 

 the branch to the right is a cluster of staminate cones. 



The staminate cone. The staminate cones are comparatively small and 

 develop in clusters near the base of the new stem soon after the be- 

 ginning of the growing season. They live for a few weeks only, and 

 wither and fall from the tree after the pollen is shed. The cone con- 

 sists of an axis on which membranous cone scales, or "microsporo- 

 phylls," are arranged spirally. Each microsporophyll contains on the 

 under side of its scale-like portion two microsporangia (pollen sacs). 

 Within the microsporangia are the microspores which later become 

 pollen grains. 



Microspore mother cells are formed in the scarcely differentiated 



