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 that flax, hemp, and linen (all of thciu 

 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 Coniferae, and serves as an excellent microscopical character for fossil 

 woods. 



FiBRo-vAscuLAR TissuE {Trachenchymd) 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 Vessels {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 Pleiotrachea?. 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 tracheae. 



Spurious Trachea, or ducts, ai'e 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 

 scahtriform 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 Vasiform Tissue {Bothrencfiyma, 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 appcai-ance. 



5 



