434 



Tin; VASCULAR PLANTS 



have germinated as internal parasites and thus the female 

 gametophytes have been produced. One gametophyte 

 matures in each megasporangium. It produces two or more 



eggs. (See Figure 226.) 

 The sperms are in the 

 pollen and the eggs are 

 in the megasporangia. 

 How are they to be 

 brought together? 



C. The Pollen Tube. 

 - You have learned of 

 pollen tubes in your 

 study of the flower. 

 You know that they 

 grow down through the 

 styles, penetrate the 

 ovary, and that by 

 means of them the 

 sperms finally reach the 

 eggs. Butgymnosperms 

 have neither ovaries nor 

 styles. Their ovules 

 are borne on the surface 

 of the sporophylls and 



the pollen comes directly in contact with them. None the 



less, pollen tubes are needed and pollen tubes are produced. 



They are needed to penetrate that tissue of the ovule which 



separates the sperm from the egg. 



D. The Embryo. After fertilization the pine cone en- 

 larges until it reaches that full size with which you are most 



FIG. 225. A, seed-bearing pine cone (stro- 

 bilus), cut so as to show the relation of the 

 seeds to the scales (megasporophylls). B, a 

 young scale showing the position of the two 

 ovules (megasporangia). C, the two- winged 

 seeds which develop from the ovules shown 

 as they lie upon the inner face of the scale. 



