SPERMATOPHYTES : GYMNOSPERMS 



183 



called siphonogamy, which means " sexual reproduction by 

 means of a tube." So important is this character among 

 Sperniatophytes that some have proposed to call the group 

 Siphonogams. 



102. Development of the embryo. — The oospore when 

 formed lies at the surface of the endosperm (female gameto- 

 phyte) nearest to the micropyle. As the endosperm is to 

 supply nourishment to the em- 

 bryo, this position is not the 

 most favorable. Therefore, as 

 in Selaginella, the oospore first 

 develops a suspensor, which in 

 pine and its allies becomes very 

 long and often tortuous (Fig. 

 153, A, s). At the tip of the 

 suspensor the cell or cells (em- 

 bryo cells) which are to develop 

 the embryo are carried (Fig. 153, 

 A, Tea), and thus become deeply 

 buried, about centrally placed, 

 in the endosperm. 



Several suspensors may start 

 from as many archegonia in the 

 same ovule, and several embryos 

 may begin to develop, but as a 

 rule only one survives, and the 

 solitary completed embryo (Fig. 

 153, B) lies centrally imbedded 



in the endosperm (Fig. 153«). The development of more 

 than one embryo in a megasporangium (ovule) is called 

 polyembryony, a phenomenon natural to Gymnosperms with 

 their several archegonia upon a single gametophyte. 



103. The seed.— While the embryo is developing some 

 important changes are taking place in the ovule outside 

 of the endosperm. The most noteworthy is the develop- 

 ment of a special tissue that forms a hard bony covering, 



Fig. 153. Embryos of pine: A, 

 very young embryos (Jed) at tbe 

 tips of long and contorted sus- 

 pensors («); B, older embryo, 

 showing attachment to suspen- 

 sor (#), the extensive root sheath 

 (wh), root tip (ws), stem tip 

 (v), and cotyledons (c).— After 

 Stbasburger. 



