402 ABIETINEAE [CH. 



sclerous tissue in the ground-tissue of the leaf and a complete 

 absence of mesophyll with infolded walls like that of recent and 

 some fossil Pines (c/. fig. 774). The phloem is represented by a 

 crescentic space in the leaf shown in fig. 791, A. The dark zone 

 surrounding the bundle consists of thick-walled and relatively 

 long transfusion-tracheids and external to these is a broader sheath 

 of short transfusion-tracheids, but there is no endodermal layer 

 and no admixture of parenchyma with the tracheids. The xylem 

 is composed partly of centripetal and in part of centrifugal elements : 

 the centrifugal xylem forms an uninterrupted arc next the phloem, 

 and between this and the transfusion-tissue on the lower side of 

 the bundle seen in fig. 791, A the centripetal xylem is represented 

 by radial rows of tracheids separated by spaces. Spiral proto- 

 xylem elements occur between the two groups of metaxylem. It 

 is interesting to find similar transfusion- tissue in some leaves of 

 true Pines described by Jeffrey from the same beds, but their 

 bundles are double and composed of centrifugal xylem only as in 

 modern species. 



The pith of the axis of a Prepinus shoot contains nests of 

 sclerous cells: the leaf -traces pass through the cortex as single 

 bundles, and the single ring of wood contains a row of resin-canals 

 blocked by tyloses. The tracheids have imiseriate bordered pits 

 which are often contiguous and separated by Sanio's rims. 



Jeffrey compares this species with Pinites {=Pityites) Solmsi 

 Sew.^ (fig. 772) from English Wealden beds and with shoots 

 described by Fontaine^ from the Potomac series under Heer's 

 generic name Leptostrohus. 



Prepinus viticitensis Jeffrey. 



This species^ was founded on specimens of short shoots from 

 the Lower Cretaceous clays of Gay Head, Martha's Vineyard, 

 Massachusetts, which are considered to be closelv allied to Pityites 

 Solmsi. The wood of the axis, representing a single year's growth, 

 contains two series of resin-canals and, as in the tvpe-species, the 

 canals of the leaves are in continuity with those in the cortex of 

 the shoot-axis, whereas in recent Pines the leaf-canals end blindly. 



1 Seward (95) A. p. 196, Pis. xvni., xix. See page 373. 



2 Fontaine (89) B. p. 227, Pis. ci.— civ. etc. a Jeffrey (10). 



