1Q15] AASE—MEGASPOROPHYLLS OF COXIFERS 311 



The ovule of Phyllocladus glauca presents a slightly simpler 

 situation than that of Taxus. The two bundles beginning from the 

 sides of the gap and ending at the base of the ovule are probably the 

 only vestige of the scale. The aril may be no more than an out- 

 growth such as appears in connection with the ripening of ovules 

 in the podocarps. The outer integument of Torreya may be a 

 more complex organ. 



If any probable conclusions can be made concerning the ovulate 

 structure of the Taxineae, they must in any event be preceded by a 

 more thorough investigation of the different forms. 



In spite of striking modifications, the origin of the megasporo- 

 phyll is homologous throughout the conifers. As to the identity 

 of the organ in question there seems nothing new to be added. 

 The gradation from foliage leaves to bracts of sporophylls is so 

 definite in many forms, as in Larix and Pseudotsuga, that the 

 homology of one with the other need not be questioned. The scale 

 is the organ in doubt. Its axillary position and the origin of the 

 vascular supply when separate from that of the bract justifies 

 the theory that it is some modification of a fertile branch. Through 

 shortening of the axis and rather delayed development of the shoot 

 in general, together with a relatively earlier development of the 

 ovules, the semicircle of bundles at the base of an ordinary shoot 

 failed to form the cylinder, but instead flattened out into an arc 

 and in some cases even into a straight line. 



Summary 



1. In the evolution of the ovulate strobilus in members of the 

 Coniferales, two general tendencies are apparent: (1) the reduc- 

 tion in number of sporophylls in the strobilus; (2) the modification 

 of a compound sporophyll into an apparently simple sporophyll; 

 the latter appears in diverse disguises, but in general implies loss 

 of one of the sporophyll members or welding of the two. 



2. Strobilus reduction has reached its highest expression in 

 members of the Cupressineae, Taxineae. and Podocarpineae; one 

 type of strobilus reduction is represented by the general sterilization 

 and reduction of parts in the lower sporophylls of Pinus. 



