BUNDLE-ENDS 



3G7 



in Picea excelsa and in the genus Pinus, finally, the whole vascular 

 strand is surrounded by transfusion tissue. As De Bary first pointed 

 out, this transfusion tissue consists of parenchymatous tracheides, with 

 pits of the bordered type. In the Cupressineae the walls of the trans- 

 fusion tracheides are provided with peculiar peg-like projections, while 

 in other cases they are furnished with spiral or reticulate thickenings. 



Fig. 147. 



Bundle-ends. A. L.S. through a bundle-end from one of the leaf-teeth of Fuchsia 

 globosa; u, transitional cell; s, sieve-tube; c, phloem-parenchyma cell (cambiform 

 cell). B. T.S. through a bi-collateral bundle-end from the lamina of Bcballium 

 Elaterium ; t, tracheide ; I, conducting parenchyma ; e, phloem -parenchyma (cambi- 

 form cells); s, sieve-tubes ; g, companion cell ; w, transitional cell (exceptionally large 

 companion cell). C. T.S. through a bundle-end from the lamina of Aralia Sieboldii ; 

 t, tracheide ; I, conducting parenchyma ; s, sieve-tube ; g, companion cell (transitional 

 cell) ; i, secretary intercellular passage. 



According 



to Scheit, these thickenings are most strongly developed 

 where the transfusion tissue abuts directly against photosynthetic 

 parenchyma. If, on the other hand, the transfusion tissue is contained 

 within a thick-walled parenchymatous sheath as in Pinus and other 

 Abietineae the walls of the tracheides do not require to be specially 

 strengthened, and therefore only bear bordered pits. Scheit states that 

 the quantitative development of the transfusion tissue depends upon the 



