THE PRINCIPAL TISSUES. 



81 



Eehinocystis, Ecbalium, Vitis, Bignonin, and Calamus Rotang ; also 

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

 Osmunda, Equisetum, and Lycopodium. 



(6) 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. 



Pig. 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 ' the sieve plates are 

 Keen in front view ; at c, c, they are seen in section ; the tube s 2 has sieve plates 

 on its right and left walls, but none on its further wall, which is in contact with pa- 

 rcnchyma-cdls ; two of the latter are seen to have nuclei in them, x 375. After i)e 

 Bary. 



1O7. Tracheary Tissue. Under this head are to be 

 grouped those vessels which, while differing considerably in 

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

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



