GYMNOSPERM^E. 



129 



Tribes. 



Genera. 



characteristics of Abies, Tsitga, Picea, Cedrus, and Larix seem to blend and lose them- 

 selves in these ancestral species. 1 The types which were formerly the most widely spread 

 now extend farthest to the south. 



The structural characters of the cone are especially important in this tribe. The 

 support of the ovule represents an axillary shoot reduced to a single phyllode, supporting 

 two ovules, and is only slightly and superficially soldered to the bract. After fertilisation 

 this support alone increases in size and forms the scale of the cone, while the bract dies 

 away or presents no appearance different to an ordinary leaf. The ovules are always 

 inverse and buried in the substance of the scale, usually becoming surrounded with a 

 membranous wing formed from its outer cellular layer. The general appearance and 

 later history of the tribe have already been described (p. 60) in this Memoir. 



With the Cretaceous, or rather with that indefinite age which intervened between the 

 close of the Cretaceous and the dawn of the Eocene, unrepresented by any stratified rocks 

 in England, we close the book on the evolution of Gymnosperms, for nearly all the archaic 

 anomalous genera which held the place of our Larches, Pines and Spruces, Cypresses, and 

 Junipers, give way to living genera and even species. 



1 The following simple classification of the Abietinese proposed by Saporta seems specially applicable 

 to the needs of the geologist. 



Sub-genera, 

 f Strobus. Leaves fasciculated by fives ; apophyses terminal ; 



scales of cone persistent. 

 Cembra. Leaves fasciculated by fives ; apophyses terminal ; 



scales of cone caducous. 

 Pseudo-strobus. Leaves fasciculated by fives ; apophyses central ; 



scales of cone persistent. 

 Teeda. Leaves fasciculated by threes ; apophyses central ; 



scales of cone usually caducous. 

 Pinaster. Leaves fasciculated in twos ; apophyses central ; 



scales of cone persistent or caducous. 

 Leaves caducous ; cone pendent ; scales loosely im- 

 bricated, detaching themselves from the axis on 

 maturity. 

 Leaves caducous ; cone erect, with scales persistent. 

 Leaves perennial ; cones with scales detaching them- 

 selves from the axis at maturity. 

 f Abies vera. Cones erect ; scales detaching from the axis at 



maturity ; bracts more or less visible, persistent at 

 the base of the scales. 

 Cones small, terminal, pendent ; scales few and per- 

 sistent ; leaves relatively broad and short, regularly 

 distichous. 

 ___ Pseudo-tsuga. Cones terminal, with persistent scales ; leaves very 

 linear and irregularly distichous. 

 Leaves inserted on elevated cushions and decurrent. 



PlNEiE. PlNUS 



Larice^e 



rPsEUDO-LARIX 



j Larix . . 

 ^Cedrus . . 



f Abies. 

 Leaves inserted 



SaPINEjE < 



direct, and leav-^ Tsuga 

 ing a discoidal 

 cicatrice 



^Picea 



