Kaloxylon Hookeri and Lyginodendron Oldhamium. 113 



the specimen, and it will be noticed that, as is the general 

 rule in recent roots, it arises endogenously at the periphery 

 of the stele and stands opposite to one of the xylem plates. 



Coming now to the last series of specimens, we find 

 quite a number of root characteristics, which appear to be 

 conclusive of their morphological nature. In the figures 

 given by Williamson in the Vllth* and Xllltlrf- Memoirs 

 there are no indications that the centrifugally developed 

 secondary xylem is superimposed on a stele whose structure 

 is that of a typical root, unless it be the last, and even this 

 is not free from ambiguity. But in several specimens which 

 have passed through my hands this is clearly shown, and in 

 the Cash Collection of Fossil Plants at the Manchester 

 Museum, Owens College, there is one preparation which is 

 demonstrative! In this the steleor central cylinder is hexarch 

 but two of the initial points of development of the xylem are 

 very near to one another. The six groups of protoxylem are 

 still easily distinguishable, and the original six xylem plates 

 can be made out without much difficulty, embedded in 

 conjunctive parenchyma. § The secondary xylem consists of 

 five broad, nearly oblong masses and a much smaller sixth, 

 each standing opposite the sinus between two plates of the 

 primary xylem, while opposite the latter are broad medullary 

 rays, which widen as they approach the cortex. || A lenticular 

 mass of phloem, normally placed externally, accompanies 

 each mass of secondary xylem, so that the secondary 

 bundles are collateral. IF Enclosing the ring of collateral 

 bundles, are two or three layers of cells, which are not well 

 preserved, but which certainly differ from those of the 

 cortex. These I take to be the representatives of the 

 pericycle and endodermis. 



The cortex retains its primary structure for some time 



* Phil. Trans., 1876, PL 5, Figs. 2, 3, and 26 and PI. 7, Figs. 37, 38. 

 \Phil. Trans., PI. 23, Figs. 20, 26.' J PI. II. Fig. 1. § Fig. 1. a. |] Fig. 1. 

 b. m. IT Fig. 1. p. 



