THE GYMNOSPERMAE : CONIFERALES AND TAXALES 679 



to form a compound strobilus. All stages of reduction from this condition 

 to that of a simple cone may be found within the genus. 



Whatever explanation is adopted it should apply to all Coniferales, as the 



Fig 679.-F0SS1I progenitors of the Pima cone scale. A, Coydmtes 

 pseudofluitans, female strobilus. B, W alchia germamca, conYC^le with 

 C ovules and tvv'O stenle appendages. C, Pseudovoltzw hebeana, cone 

 scale with t^vo o^'ules and five sterile appendages. D, Modern Pine 

 tvpe, with two o^oiles and single stenle appendage, forming an 

 ovuliferous scale. {After Wilde.) 



female cones appear to be homologous throughout the order. The peculiarity 

 of Pinus lies merely m the well-marked separation which exists between the 

 two types of cone scale, but a duality of nature can be traced m the vascular 

 anatomy of all cone scales, even those in which the two components seem to 

 be most closely united. 



/ntegument 



Nucellus 

 Embryo sac 



Ovuliferous scale 

 Bract scale 



Fig. eSo.— Pinus svlrestris. Vertical tangential section of 

 a female cone scale passing through the two ovules and 

 showing the position of the bract scale. 



On the upper surface of the ovuliferous scale two ovules are produced side 

 by side (Fig 680). Each arises as a group of cells which forrns a rounded 

 hump of tissue termed the nucellus. This is rapidly surrounded by a two- 

 lipped, covering laver termed the integument, which grows up around it 

 starting from the outer (abaxial) end of the nucellus and growing inward? 



