BOTANY. 5 
These overlap each other, and are so combined as to give great strength and 
firmness to the plant. It differs from simple cellular tissue in its cylindrical 
and elongated form. The term Prosenchyma is properly applied to short 
fusiform cellular tissue. Woody tissue is found in wood, in the inner bark, 
and in the skeleton of the leaf, and may be,separated from the other portions 
of the plant by maceration. It is thus tha fax, hemp, and linen (all of them 
forms of ligneous fibre) are obtained. Cotton, on ‘the other hand, consists of 
elongated cells or hairs, which collapse on drying, and twist spirally, as seen 
under the microscope, this constituting an excellent test to distinguish the 
latter from the former. Common pleurenchyma presents no markings; in 
glandular, on the other hand, the tubes exhibit discoid depressions on the 
outside of the wall. The depressions of two contiguous tubes are generally 
opposite to each other, and thus inclose a doubly convex lenticular space. In 
some cases there is a secondary depression in the bottom of the primary, 
which, when viewed by transmitted light, appears as a light circle inside of 
a darker one. This glandular or punctated woody tissue is exhibited in all 
the Coniferze, and serves as an excellent microscopical character for fossil 
woods. 
Fisro-vascutar Tissue (Trachenchyma) consists of tapering membra- 
nous tubes, and having either a spiral fibre inclosed, or else markings of rings, 
dots, or bars, arranged in a more or less spiral form. ‘This tissue occurs 
especially in the medullary sheath, and in the veins of the leaves. True 
SpiraL Vessets (Spiroidea) exhibit themselves as elongated tubes, over- 
lapping at the conical extremities, with a spiral fibre on the inside, not on 
the outside, as has been erroneously stated. The thin outer membrane con- 
sists of pure cellulose. The point where two successive spiral vessels overlap 
is sometimes absorbed, so as to present a free communication. The internal 
fibre is generally single ; more rarely a greater number, as, from two to twenty 
are combined, so as to present a band constituting Pleiotrachee. The spiral 
generally turns from right to left. The coils may be separated or united: this 
union among each other, and to the sides of the vessel, may be so close as to 
constitute closed tracheee. 
Spursous TRacHE#, or ducts, are vessels in which the internal spiral is 
broken up and variously modified. A principal variety is the annular, where 
the broken coils are combined into rings, which may be horizontal or oblique, 
simple or branched, contiguous or remote. In reticulated vessels separate 
fibres run into each other on the walls of the tube ; when the fibre is broken 
up into short pieces which adhere to the walls, the vessel becomes dotted. In 
scalariform vessels the pieces of the fibre are shorter, and passing transversely, 
and nearly parallel across the vessel, present an appearance not unlike that of 
the rounds of a ladder. Such vessels are generally prismatic, as in Ferns, 
the angles being unmarked. 
In Vasirorm Tissue (Bothrenchyma, or Taphrenchyma), the vessels 
exhibit an appearance of pores on the surface. These vessels consist of 
cylinders, more or less elongated, in which the thickening matter is so 
deposited as to leave part of the membrane uncovered, thus causing the porous 
or pitted appearance. 
5) 
