THE PRINCIPAL TISSUES. 



81 



Eehinocystis, Ecbalium, Vitis, Bignonia, and Calamus Botang j also 

 Abies pectinata, Larix, Juniperus, Sequoia, and Ginkgo ; also Pteris, 

 Osmunda, Equisetum, and Lycopodium. 



(b) By making repeated horizontal sections the horizontal sieve discs 

 may be found and studied. 



(c) Alcoholic specimens afford much more satisfactory results than 

 fresh ones ; especially is this the case with the more succulent plants. 



Fig. 71. — Sieve tissue of Pteris aquilina. A, end of a sieve tube isolated by macer- 

 ation : B. portions of two tubes seen in vertical section ; in s' the sieve plates are 

 seen in front view ; at c, c, they are seen in section ; the tube s^ has sieve plates 

 on its right and left walls, but uone on its further wall, wnich is in contact with pa- 

 renchyma-cells ; two of the latter are seen to have nuclei in them, x 375. — Alter Be 

 Bary. 



107. — Traeheary Tissue. Under this head are to be 

 grouped those vessels which, while differing- considerably in 

 the details, agree in haying thickened walls, which are perfo- 

 rated at the places where similar vessels touch each other. The 



