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VEGETATIVE FEATURES. 



of cycads, nature seems invariably to have seized upon the reproductive organs and 

 to have found them the most plastic and susceptible of change. In the one case 

 the much greater change went on in the megasporophylls, and there was evolved 

 a form of true flower exactly suggestive of the types of change in reproductive 

 organs that resulted in the augiosperms. In the other both types of sporophylls 

 were seized upon and carried forward through the same stages of reduction, save 

 for that single, wonderful, and marvelous survival from the Paleozoic, that analogue 

 of the staminate frond, the carpophyll of Cycas. 



CORTEX. 



GENERAL FEATURES. 



In the existing cycads, as was first fully described by Mettenius (92), in order 

 to supply each leaf base, two bundles take their origin near together on the stele or 



woody cylinder, and then curve round the 

 trunk in opposite directions, thus passing 

 outward and upward through the cortex 

 for a long distance, in some forms nearly 

 180 , or quite to the opposite side of the 

 trunk, before entering the leaf base. Here 

 subdivision takes place, the resulting bun- 

 dles soon aligning themselves, as has just 

 been fully illustrated, in an omega or else 

 a circular order, as seen in transverse 

 sections. All along the course of the 

 curving traces through the cortex there is 

 much anastomosing, not only between 

 bundles of the same leaf base, but between 

 those of different leaf bases, as well as 

 with the woody cylinder. The peduncle 

 traces, owing to the apical position of the 

 cones, pass in to the medulla, the trunk 

 literally growing through and past them. 

 Traces of simpler structure are not, however, wanting in very young trunks ; but 

 in view of the generally complex development of the cortical region it is of the 

 highest interest to determine to what extent variations from a simple structural 

 type may have been present in the Cycadeoidese. 



Very clearly the course of the leaf traces of the existing cycads is a recent 

 development, possibly of post-Cretaceous origin, bearing in mind the simpler type 

 of all the fossil forms known, as well as the fact of deviation from the simpler more 

 fern -like cycadofilices. Consequently it can not be expected that amongst the 

 Cycadeoidese any strongly marked departure from simple types will be found. For 

 generally considered the lateral peduncles, or fruiting branches, certainly find a not 

 very remote analogue in the small and often numerous scale-leaf-beariug branches 

 of Cycas; whence it may be said that the cycadeoidean trunks, aside from the order 

 of the fruit-bearing branches, only differ at all widely from those of the existing 



Fig. 35. — Cycadella sp. 



Transverse section through the summit of a small silici- 

 fied trunk from the Freezeout Hills, Carbon County, 

 Wyoming, showing the medulla, woody cylinder, 

 cortex, and a portion of the enveloping armor of old 

 leaf bases. Natural size. 



m, medulla ; x. xylem ; c, cambium; p, phloem; ft, leaf (or 

 peduncle) traces arising from the xylem or woody cylinder ; 

 cb, horseshoe-shaped cortical bundles, or leaf traces ; 1. 

 insertion of leaf base in cortex; r. ramentum of leaf bases. 



