32 STIGMARIA FICOIDES. 



that bundle, and their smaller size is due, as has already been explained on p. 22, 

 to the fact that they have been derived from a younger layer of half- developed 

 Tracheids like that seen at V in Plate IV, fig. 19. 



An invariable vegetative repetition of so complex an organisation as I have 

 now described appears to be absolutely incompatible with the possibility of some 

 of the organs so constructed being phyllomes and others caulomes or emergences 

 from caulomes. That members with such different functions as leaves and roots 

 should possess so absolutely identical a structure, form, and direction of growth 

 seems to me too absurd to be conceived. 



In several instances I have met with clusters of rootlets, a transverse section of 

 one of which is represented in Plate XIII, fig. 79, where each rootlet has a thin 

 longitudinal cellular lamina, fig. 79, /", looking like a centripetal extension of the 

 outer cortex, g, of the rootlet, and connecting that cortex with the bundle cylinder, 

 /. In many such examples the lamina appears to join the bundle cylinder exactly 

 opposite the point of departure of the bundle from its cylinder. I am not yet, 

 however, quite sure that this is a constant relationship between the position of the 

 lamina and the acropetal side of the rootlet. 1 



Plate XI, fig. 62, is a transverse section of a young rootlet with only three or 

 four xylem Tracheids,/, but we find at /"the phloem cells of the bundle occupying 

 the position which I have assigned to the phloem in Plate V, fig. 48, /', and 

 Plate IX, fig. 52,/. 



Plate XIII, fig. 27, and Plate XI, fig. 63, illustrate another feature occasionally 

 seen in these rootlets. Artis long ago represented some which were dichotomous 

 at their free extremities, 2 and Corda figured a similar example. 3 Plate XIII, 

 fig. 27, represents a similar dichotomous form, such specimens being occasionally 

 met with in our Lancashire deposits. Besides this my cabinet contains several 

 transverse sections of what have been rootlets either preparing for or actually 

 undergoing similar dichotomy. Plate XI, fig. 63, g, represents the inner surface of 

 the external cortical zone of the rootlet, within which is the usual fistular cavity, g '. 

 But at // we have two bundles that have originated from the subdivision of a 

 primary one, each being enclosed in its separate bundle cylinder, /. The cortical 

 zone, g, has not yet shared this dichotomy, but in another of my sections it has 

 done so. In it a broad belt of the cortical tissue g has extended completely across 



1 M. Renault has figured a rootlet bundle with its bundle sheath, from the exterior of which a 

 similar cellular band radiates ; but he thinks he sees in the specimen evidence that a lateral branch 

 (radicelle) springs from the rootlet as well as that the rootlet bundle is double, half of which 

 is developed centripetallj, and the other half centrifugally. Nothing of this kind exists in any one of 

 the innumerable rootlets in my cabinet. That a few of them dichotomise is shown in PI. XIII, fig. 27, 

 but such dichotomy is invariably truly terminal, not lateral or monopodial. 



2 ' Antediluvian Phytology,' Ficoidites furcatus, PI. iii, a, b. 



3 ' Flora der Vorwelt.' Taf. xii, fig. 1, a. 



