74 MICROSCOPIC OBJECTS. 



consist of membranous tubes with conical extremities, 

 internally furnished with one or more spiral fibres. As 

 the vessels grow, the spu'al fibre breaks into short pieces, 

 forming rings : the vessels are then called annular : if 

 the pieces of fibres are still shorter, they are called dotted 

 or reticulated vessels. Much discussion has arisen among 

 botanists as to the form of the fibre ; that is, whether it 

 be round like a cord, or flat like a ribbon. The root of 

 the hyacinth and the stem (petiole) of the common gar- 

 den rhubarb, the latter even after it has been cooked, 

 peld spiral vessels in abundance. 



Dotted Vessels. — A peculiar form of vessel is met with 

 in the common Carrot ; it is obtained from the root in 

 a layer between the yellow central portion and the red 

 annulus. As a microscopic object it is very interesting. — 

 Power 150 diameters. 



Woody Fibre. — This form of tissue may be readily 

 examined in the examples given in the Catalogue, it being 

 separated from the other elementary organs. The form 

 of the woody fibres of flax (of which our best linens are 

 made) is that of solid cy finders ; hence the durability of 

 those fabrics. The diameter of the fibres varies greatl}- : 

 in some of the Coniferae it exceeds ^^^th of an inch, 

 while the fibres used in making the threads for the fine 

 French cambric are about -g-Jo^^ °^ ^^ "^^^• 



Woody Fibre glandular. — On the sides of the w^oody 

 fibres of the trees named in this division are small disc- 

 shaped glands : they are disposed in rows, and are best 

 seen in a radial vertical section of the w^ood. These 



