298 GYMNOSPERMS 



the genera have more or less anatropous ovules, while, in the other 

 half, they are more or less orthotropous. 



The free condition is regarded as primitive, and the more or less 

 "united" condition as more advanced. It must be remembered that 

 both conditions existed in the early gymnosperms of the Carbonifer- 

 ous. In Trigonocarpus the nucellus was entirely free from the integ- 

 ument, while, in the best-known of all paleozoic seeds, Lyginopteris 

 {Lagenostoma) , the "union" was almost complete. 



Fig. 302. — Pinusbanksiana: bract; ovuliferous scale; and ovule. The bract and scale, 

 in such a condition, are said to be free from each other; X25. 



Nowhere in the order is there any extensive vascular system in the 

 ovule, like that of the cycads. In most cases, there are no bundles at 

 all in the integument, or in the aril, where this structure is present. 

 In Microcachrys and Saxagothca there are bundles at the base of the 

 integument, and, in Podocarpus, bundles sometimes extend almost 

 to the top of the integument. 



While there is not such a difTerentiation of the integument into 

 strongly marked regions, as in the cycads, three regions are often 

 distinguishable, a middle layer which becomes hard, with a fleshy 

 layer on each side. The outer layer may remain fleshy for a longer or 

 shorter time, while the inner, fleshy layer always becomes dry and 

 membranous. 



The mcgasporangium, throughout the order, is eusporangiate and 

 massive, and shows great diversity in its appearance (figs. 302-6). 



