﻿EXISTING AND FOSSIL CYCADS COMPARED. 



silicified strobili, as has been seen, the peduncle is large and the bracts prominent 

 long before the sporophylls appear. In such stages, then, there is well-nigh complete 

 similarity to the lateral buds of Cycas, There is hence on the one hand the power 

 to develop as a fruiting branch and on the other as a vegetative branch, or if 

 detached a separate trunk. But that lateral buds of the Cycadeoideae, as scarcely 

 distinguishable from strobili in their earlier stages, also developed as branches may 

 further be assumed. It is, then, fairly evident that the feature seized upon by the 

 cycadeoidean line as a means of progression, or perchance necessity for the produc- 

 tion of more numerous seeds — these having already reached a high organization- 

 was the lateral branch or bud. This was theu segregated as a branch of solely repro- 

 ductive function. On the other hand, the surviving cycads, Cycas excepted, do not 

 now exhibit a truly monopodial habit, although branching is common and the 

 incipient monopodial stages are obviously 

 present. The cones having remained few 

 in number, are produced for the greater 

 part sympodially at or near the summit, 

 although it is entirely possible that more 

 cones, extending farther down the sides 

 of the trunk, were present in past time 

 or in certain extinct genera. It is hence 

 easy to conceive of hypothetical genera 

 falling within the cycadeoidean and exist- 

 ing cycad groups, which would bring the 

 branching features and stem habit of the 

 one group into complete touch with the 

 other ; and that there is present, so far as 

 such habitus features go, a fundamental 

 similarity throughout all of the known 

 evcadaceous forms is an inevitable con- 

 clusion. 



The cycadeoidean microsporophylls are reduced pollen-bearing or staminate 

 fronds of Marattiaceous derivation, antithetically homologous to the megasporo- 

 phylls of Cycas — such is our conclusion. But while their form is unquestionably 

 normal to primitive cycads in every respect, their arrangement in a disk is mainly 

 characteristic ofangiosperm stamens and unique to the cycads, though not entirely 

 so to gymuospenus, since in Tumboa {Welwitschia mirabilis) the most reduced of 

 all gymuospermous sporophylls are likewise organized into staminate disks. As the 

 cycadeoidean disk is epygy nous to the spiral of enveloping bracts, in turn regarded 

 as reduced fronds, the simplest view of its meaning and origin is that it is derived 

 from a lateral and basal fusion of the members of a closely set whorl or spiral at 

 first placed much like that of the leaves of Sciadopitys. An original 5/13 arrange- 

 ment is perchance suggested by the fact that the disk of Cycadeoidea ingens and 

 Cycadella is composed of thirteen fronds, and some higher form like 21/55 by C. 

 dacotensis with an eighteen-frond disk. Possibly when fusion took place in the 



133. — Welwitschia mirabilis or Tumboa. Single 

 flower of cone- like inflorescence with enveloping 

 scale and bracts removed to show essential organs, 

 consisting in a staminate drsk or androecium inclosing 

 the central abortive megaspore. This flower is hence 

 morphologically but not functionally bisporangiate. 

 It is the only surviving example of true cyclic 

 arrangement in the gymnosperms. 



The figure is greatly enlarged. (From Engler und Prantl. 

 after Strasburger.) 



