290 Hill . — The Histology of the Sieve-Tubes of A ngiosperms. 
PLATE XVIII (Figs. 59-62). 
Tilia vulgaris. 
Fig. 59. A sieve-tube in transverse section, showing the difference between the sieve-fields in the 
tangential and radial walls. In both cases they show median nodes, but in the tangential walls the 
connexions are very numerous and delicate. Callus is found in both cases, but is not indicated in 
the figure, x 1,000. 
Fig. 60. A sieve-tube with two companion cells in transverse section. With Russow’s callus- 
reagent, small callus- rods are seen in the sieve-tube half of the wall between companion cells and 
sieve- tubes, x 1,000. 
Fig. 61. A tangential wall between two sieve-tubes in surface view, showing the vast numbers of 
threads or fine slime-strings arranged in little groups, x 750. 
Fig. 62. A wall between a sieve-tube and a bast parenchyma cell in longitudinal section. 
A callus-pad is seen on the sieve-tube side over the groups of threads, but it could not be seen 
whether the callus extended to the lamella. Small median dots are seen on the threads. Winter 
material, x 1,000. 
