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A TEXTBOOK OF THEORETICAL BOTANY 



occur in the cone scales of other Gymnosperms in which fohar spurs are 

 unknown. 



Variations of this theory are numerous. For example, Van Tieghem 

 held that only one leaf of the axillary shoot was involved, namely the one 

 which stood uppermost, opposite the bract. Zimmermann, on the other 

 hand, concluded that the axillary shoot which has become the ovuliferous 

 scale was entirely sporangiferous, and has been reduced from a multiovulate 

 condition to the present condition with two ovules only. 



The principal opposing theories have been : — 



1. Sachs and Eichler. The ovuliferous scale is an outgrowth of the 



bract scale, comparable to a ligule or placenta. 



2. Kubart and Bessey. The ovuliferous scale is a combined outgrowth 



of the ovules themselves, and might be called an aril or an enlarge- 

 ment of the chalaza of the ovules. 



3. Delpino. The ovuliferous scale is formed from two lateral lobes 



of the bract scale which have been turned inwards and fused 

 together. 



4. Hirmer. The ovuliferous scale and the bract scale are both parts 



of one structure, which has forked vertically in the same way 



as the sporophylls in Cheirostrobiis and other Sphenophyllales 



may have forked. 



The extensive researches of Florin on the fossil Conifers may be regarded 



as giving decisive evidence in favour of 



the compound theory of the cone, which 



regards it as an inflorescence and the 



ovuliferous scales as short shoots. 



The genus Psendovoltzia (Permian) 



1^"^ showed bract scales subtending an axial 



structure consisting of two anatropous 



ovules on long stalks, above which are 



five sterile bracteoles or scales. Fusion 



of the latter has produced the spur 



which is the ovuliferous scale, to which 



the stalks of the two remaining ovules 



are adnate. Later, in higher Conifers 



such as the Cupressineae, a further fusion 



of the ovuliferous scale with the bract 



scale takes place, the cone scales thus 



becoming simple, not double, structures 



(Fig. 679) (see also Volume III). 



It may be mentioned that there 



is evidence from the genus Podocarpiis 



p , „ „• ,, ^ , that the male cone was primitively com- 



hiG. 678. — Diagram to illustrate Braun s , . . ^ . ■' 



theory of the origin of the ovuliferous pound. In some species ot that genus 



scale. The ovules are shaded and the it is still compound, with simple sessile 

 axis or the primitive axiUarv shoot is ... . .. „ . 



•(^ 



)© 



marked with a cross. 



cones arismg 



in the axils of bracts 



