194 



Actinidia. Besides these, Solereder found it in Wormia {Dilleniacew). 

 Diplotaxis {Crucifer(e)-Fomiera {Tamarisc), Princepia Chmomanacem), 

 Aucuba (CornacecB, only in herbarium material), PeclaWnn [Pcdaliacew), 

 DaphnyplniUum {Daphfiupliyllacea'): AYilliamson also found it in the fossil 

 plants known as Sternhergm and mentions it as occurring in certain liv- 

 ing species of Pinns. In some genera, as e. g. Fors,itl,ia and Jasmiuum. 

 it occurs in some species but not in others. 



The cells making up the partitions are thin-walled, empty and often 

 shrunken and the space between the partitions is irregular in outline and 

 extent. Fig. 4, from a twig of Juglans cinerea, shows this type. 

 Function and manner of formation :— 



Morren and Williamson both considered that the pith served as a 

 mamilla for the bud and, as the nourishment is exhausted from the pith 

 it separates into disks-beginning first in the immediate vicinity of the 

 bud. The cells in the center of the pith become shrunken and the pith 

 separates into layers. This takes place quite early in the growing season. 

 Morren gives good figures of this process in Juglans re<jia. The fact that, 

 twigs of CeWs often have the pith very plainly discoid in the region of 

 the nodes but solid in the central part of the long internodes lends sup- 

 port to this view. 

 Taxonomic value of the occurrence of discoid pith:— 



Juglans and Pterocarya are definitely separated off from the rest of 

 the JmjhuHlacew (A. Engler in Engler & Prantl-Nat. Pfianz. Fam. 111. I. 

 p 21) by the possession of discoid pith. In Liriodendron. Asimina. Nyssa 

 Cents, Mohrodendron, Actinidia, and several others, the presence of dis- 

 coid pith seems a good generic distinction; but, in certain cases, as, 

 Forsythia and Jasminum, it is of only specific value. 



