SPERMATOPHYTE.S 



307 



genera and 350 .specie^ and they ait found mostly in the tem- 

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



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

 entation and give the Sporophyte the first consideration. Tliese 

 trees have roots and stems ver^' 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 ver\- pronounced a.- compared with that of most 

 Angiosperms. There are two t^•pes of cones, the pistillate or 



Fig. 153, — (a) Pollen grain; (6) same ehoH-ing6xst division; (c) poUentube; (d) sporangium 

 ehowing integument, micropyle and archegonia: ^^ J ^ame showing ensbryos; if) matureseed. 



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

 phylls (modified leaves i arranged in spirals. 



TThen 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 eaxjh macrosporangium 

 are two processes or extensions of the integument; the 

 opening between them is the micro pyle. The inner part of 

 the macrosporangium is called the nucellus and contains 

 one or more maerospores which become the female prothaUia 

 or Gametophytes. The archegonia are formed in the nucellus 

 near the micropyle (Figs. 1.52, 153). 



The staminate cones are made up of mierosporophvlls which 

 spread apart exposing two small sacs or anthers (microspo- 



