443 



Fig. 79 shows the habit of growth of a piece of Lavatera trimestris 

 stem with excrescences due to cell elongation. Fig. 80 shows the rup- 

 tured bark of Acacia pcndula, while Fig. 81 shows the same much more 

 clearly because of its magnification. 



In Malope grandi flora and Lavatera trimestris, stems and branches 

 were found bearing many long calluses on the side exposed to the sun. 

 These were caused by considerable longitudinal and radial stretching of the 

 bark and wood cells. If the callus is still young, the process usually sets in 

 by a radial and still more marked tangential stretching, at the level of the 

 primary hard bast bundles of the parenchyma cells containing chlorophyll 

 and lying between two bundles : with this increase they are pushed outward 





Fig. 82. Cross-section through a year old branch of 

 intumescence. (1-433).) (Orig.) 



ch of Acacia pendula with 



like a bow. The mechanical ring appears to be broken because the bast 

 bundles are pressed far apart and the collenchyma layers less developed. 

 In large intumescences the broken places apparently extend deeper since 

 the wood also changes its prosenchymatous elements and the cells of its 

 medullary rays into a wide meshed parenchyma. , 



Fig. 82 throws sufficient light on the processes concerned in the forma- 

 tion of the moss-like collection of intumescences in Acacia pendula; m 

 indicates the pith ; h the woodring ; c the cambium ; b the hard bast groups ; 

 e the epidermis ; .y the beginnings of elongation within the primary bark ; zv 

 the bark parenchyma cells which have become tube-like and ascend in 

 spirally parallel rows and, after breaking through the epidermis at w, 

 separate from one another like sheaves. 



) Sorauer, P., tJlier Intumescenzen. Ber. d. Deutsch. Bot. Ges. 1899, Bd. XVII, 



