﻿EXISTING AND FOSSIL CYCADS COMPARED. 225 



eylindrically-arranged bundles of the peduncle and lower portions of the axis of the 

 cone of some forms are of mesarch collateral structure, comparable to that of the 

 leaf bundles, and indicating, as determined by Scott (132), affinity with such ancient 

 types as Lyginodendron and the Poroxylese. (See figs. 130- 132.) 



Count vSolms-Laubach was, however, first led to the discovery of the presence 

 of such a fundamentally important ancient relationship by a study of the arrange- 

 ment of the vascular bundles of the cones. In speaking of the sudden transition 

 from the complicated structure of the vegetative stem to that of the simply and 

 primitively organized peduncle and cone axis, Solms says (155, p. 213): 



".Sehr merkwiirdigaber ist die Art und Weise, wie an einem und demselben Spross 

 unter plotzlicher verjiingungdes Pleromkorpers der coinplicirte vegetative Spurverlauf 

 ganz unvermittelt in den einfachen der Bliithe iiberspriugt. Dass dieser letzere eine 

 Reliquie uralter Organisation, dass er den gemeinsamen Vorfahren der Cycadeen und 

 Bennettiteen allgemein eigen geweseu sein wird, dass der vegetative Spurverlauf, wie 

 er jetzt bei ersterer Gruppe vorliegt, eine im Laufe der Zeit erworbene eigensehaft 

 darstellt, die den Gang der Entwickluug in der Richtung vom Einfachen zum Compli- 

 cirten uns vor Augen fiihrt, scheint mir eine sehr nahe liegende Annahme zu sein." 



As in the mouostelic vegetative axis, however, only centrifugal wood is present 

 in the woody cylinder of the peduncle of the great majority of the existing cycads. 

 It is in the staminate cone of Stangcria that retention of centripetal wood is most 

 marked. It first appears a little above the peduncle base, is more prominent in its 

 middle region, and finally disappears below the summit of the cone. Other cycads 

 retaining peduncular centripetal wood are Bowenia i ? and 5 ), Ceratozamia ( $ ), 

 and Zamia in part. It is very interesting that this recondite bundle form should 

 mainly persist in the mouotypic genera, which with Zamia constitute a group that 

 for other reasons might be set aside as exhibiting the greatest assemblage of 

 primitive characters of any of the existing cycads, the carpophylls of Cycas excepted. 

 In other words, these genera have proven the least susceptible to change and the 

 most liable to extinction, whence their present isolation. As already noted, mesarch 

 structure is highly developed in the stalk of the Cycas carpophylls, although not 

 yet observed in the staminate peduncles. The occasional and inconstant occurrence 

 of concentric bundles which end in the lower cortex of the staminate peduncles of 

 Stangeria and may occur in other genera has, however, been noted by Scott, and is 

 of considerable interest in the present connection. That concentric structure should 

 be retained in the bundles of a naked peduncular cortex no longer supporting 

 foliar structures, and be, as already seen, also characteristic of the sporophylls and 

 spore-bundle systems, is a correlative fact pointing to an ancient trunk form with 

 concentric rather than collateral cortical traces. For if ever any type of bundle 

 structure may be considered as of phyletic significance rather than the result of 

 homoplastic and physiologic accidence, it must surely be one finding its nearest 

 analogue in related plants known to be ancient and primitive, and at the same time 

 found to exhibit a certain constancy of persistence on the same axis in both the 

 functional and non-functional position. The conclusion is hence reached that the 

 cycadean cone could only have been segregated from a mouostelic trunk with a 



