REPRODfCTIVE ORGANS 



111 



of the moss-iil;ints is still more true 

 of the fern-plants ; while among 

 tlie seed-])lants certain spores {pol- 

 len grains) are conspiieuous (see 

 Fig. ll(J), bnt the eggs can be ob- 

 served only by special manipulation 

 in the laboratory. Seeds are neither 

 sjiorcs nor eggs, but ])eculiar repro- 

 ductive bodies Avhich the hidden 

 egg has helped to produce. 



73. Germination. — Spores and 

 eggs are expected to germinate ; 

 that is, to begin the development 

 of a ]iew ])lant. This germination 

 needs certain external conditions, 

 prominent among which are defi- 

 nite amounts of heat, moisture, 

 and oxygen, and sometimes light. 

 Conditions of germination nuiy be 

 observed most easily in connection 

 with seeds. It must be understood, 

 however, that what is called the 

 germination of seeds is something 



very different from the germination 

 of spores and eggs. In the latter 

 cases, germination includes the very 

 lieginnings of the young iilant. In 

 the case of a seed, germination begun 

 by an egg has been checked, and 

 seed germination is its renewal. In 

 other words, an egg has germimited 

 Fir. 109. A group of swim- aud produced a young plant called 

 ming cells : .i, a spore of ^j^g '•embrvo." and the cTermination 



CEdogonium (an alga") ; ' . ^ . , 



£. spores of HoWn-v (an of the SCed Simply COUSlsts 111 the 



alga); c, a gamete of continued growth and the escape of 



Fig. 108. A portion of the 

 body of a common alga 

 ( 'Edogoii'ium ), showing 

 gametfs of ^ ery uuf qnal size 

 and activity ; a ^e^y large 

 one io) is lying in a globular 

 cell, and a very small one is 

 entering the cell, anotlier 

 similar one t,s') being just 

 outside. The two small 

 gametes have hair-like pro- 

 cesses and can swim freely. 

 The small and large gam- 

 etes unite and form an egg. 



Eqnlsetum (horse-tail or 

 Bcouring rush). 



this embryo. 



