COMPARED WITH THOSE OP ANIMALS. 49 



" The esistenoe of tlie primordial utricle in a nornaal con- 

 dition in a cell," says Henfrey, " generally indicates ttat 

 the cell still retains the power of propagation, and it is con- 

 sequently always found in cambuim cells." The primordial 

 • utricle disappears soon after the commencement of the for- 

 mation of the secondary layers on the cell wall. 



All the organs of plants whatever be their form, their 

 mature, or their destination, have for their basis the same 

 immediate principle cellulose, which when deprived of all 

 foreign matter and brought to a state of purity, consists of 

 carbon and the elements of water. This general character, 

 cellulose, is the sign of the vegetable kingdom, although 

 the rule is not without exceptions, .cellulose having been 

 recently detected by Schmidt, Lowig, and KoUiker, in 

 the tunics of ascidia and other molluscous animals. 



Cellulose is closely allied to starch in its chemical com- 

 position, but differs in- giving a yCllow in place of a blue 

 color with iodine. It is generally colorless, and of a 

 whitish hue ; in some cases, however, as in ferns, it is 

 brown. When thickened by successive deposits, it pos- 

 sesses a laminated structure. It is readily permeable to 

 fluids, but without visible pores. 



Plants have, therefore, essentially for the basis of their 

 organization a ternary matter consisting of carbon, oxy- 

 gen, and hydrogen, " which exists in the liquid form in the 

 state of vegetable mucilage, dextrine, sugar, &o., or collects 

 in a peculiar solid form in the cells, as starch, or finally 

 constitutes the proper and permament wall of the cell, 

 under the name of cellulose."* Nitrogen enters sparingly 

 into the composition of plants. All the organs of plants, 

 in their first period of development, contain Nitrogen. It 



** See Gray's Botanical Text-book, p. 28. 



