SPERMATOPHYTES 



307 



genera and 350 species and they are found mostly in the tem- 

 perate zones. The pine is a good type for study. 



As a matter of convenience we will reverse our order of pres- 

 entation and give the Sporophyte the first consideration. These 

 trees have roots and stems very similar in structure to the Angio- 

 sperm plants which we have already studied. However, the 

 leaves are very much modified, ranging from flat blade-like struc- 

 tures to narrow needles. The mesophyll is greatly reduced and 

 the epidermis very pronounced as compared with that of most 

 Angiosperms. There are two types of cones, the pistillate or 



FIG. 151. (a) Pollen graiu; (6) same showing first division; (c) pollen tube; (d) sporangium 

 showing intv. ;ument, micropyle and archegonia; (e) same showing embryos; (/) mature seed. 



ovulate and the staminate, which are composed of scales or sporo- 

 phylls (modified leaves) arranged in spirals. 



When the pistillate cones are mature the macrosporophylls 

 spread apart, exposing two ovules or macrosporangia en the upper 

 surface of each. At the lower point of each macrosporangium 

 are two processes or extensions of the integument; the 

 opening between them is the micropyle. The inner part of 

 the macrosporangium is called the nucellus and contains 

 one or more macrospores which become the female prothallia 

 or Gametophytes. The archegonia are formed in the nucellus 

 near the micropyle (Figs. 152, 153). 



The staminate cones are made up of microsporophylls which 

 spread apart exposing two small sacs or anthers (microspo- 



