212 



Practical Plant Biology. 



represent the gametophyte ; the embryo enclosed in these latter 

 is the new sporophyte. In the seed, then, we have represented 

 three generations ; to these we must add the remnants of a fourth 

 individual, the pollen-tube or male gametophyte, which persists 



SELAGINELLA PLANT. 



(Sporophyte ) 



Cone. 



Mepjasporophyll Microsporophyll 



Megasporangium Microsporan^ium 



Me^aspore ^Microspore 

 Female Gametophyte 



Male Gametophyte 

 FIG. 71. Diagram summarising the life-history of Selaginella. 



Embryo 

 Oosperm 



/ \ 



Sperrn^ Ovum 



Seedling 

 .-' Embryo " 

 Oosperm 



/ XX 



I Sperm Ovum 



.-PINE TREE 



(Sporophyte) 



'Pollen-Cone 

 r Stamen 



( ' Megasporophyll) (Microsporophyll) 



OvOle"--, Pollen-Sac 



(Megasporangium'):(Microsporangium) 



Embryo -Sac Pollen-Grain': 



(Meffaspore ) (Microspore)y' 



Endosperm 



(Female Gametophyte) 



Pollen-Plant 



'-.. ( Male Gametophyte) ...-'''' 

 FIG. 72. Diagram summarising the life-history of the Pine. 



in the nucellus after fertilisation. It is a megasporangium con- 

 taining a megaspore, a female gametophyte, an embryo-sporophyte, 

 and the remnants of a microspore and male gametophyte. 



I will now chalk upon the blackboard a diagrammatic scheme 

 summarising the life-histories of Selaginella and the Pine Tree, 

 which you will find helpful in understanding the homologies and 

 relations of their various parts. 



