194 



Actinidia. Besides these, Solereder found it in Wormia (Dilleniacece), 

 Diplotaxis (Crncifer(e)-Fouqiera (Tamarisc), Pi'incepia Chri/sobalanacecs), 

 Aucuha (Cornaceic, only in herbarium material), Pedaliiim (Pedaliacew) , 

 DaplnujphyUum {Daphnyphyllacea:): AYilliamson also found it in the fossil 

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

 ing species of Finns. In some genera, as e. g. Forsijthia and Jasmininn, 

 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 Jufjlans 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 ,hir/lans ref/ia. The fact that 

 twigs of Celtis 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 Juglandacew (A. Engler in Engler & Prantl-Nat. Pflanz. Fam. 111. I. 

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

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

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

 Forsythia and Jasmimtm, it is of only specific value. 



