226 A TEXT-BOOK OF BOTANY. 



layer of the wall in which the decomposition takes place has been 

 termed by Tschirch a resinogenous layer. 



The cells or receptacles which contain oils, resins, gum-resins, 

 and balsams are usually referred to as ' secretory cells ' or 

 " secretory receptacles." The latter term is used by Solereder to 

 include all cells, cell fusions, cavities or canals which are filled 

 with secretions. Usually no attempt has been made to determine 

 whether the secretion is a volatile oil or a resin, or a gum-resin 

 or a balsam, as the appearance of the secretion is always either 

 in the form of globules or more or less rounded masses. Secretory 

 receptacles may arise in three different ways. ( I ) As a modi- 

 fication of the intercellular substance and an enlargement of the 

 intercellular areas, giving rise to schizogenous receptacles (Fig. 

 122). (2) As a result of a disintegration of a group of cells 

 and a decomposition of the wall substance, forming lysigenous 

 receptacles (Fig. 123). (3) They may have at the outset a 

 schizogenous origin, but later the surrounding cells in addition 

 break down, so that the receptacle is more properly designated as 

 being schizo-lysigenous. In certain plants, as in the bark of 

 Sassafras and Cinnamon, there is a more or less even distribu- 

 tion of cells in the cortex, containing volatile oil, on the one hand, 

 and mucilage, on the other. Indeed, it is supposed that the cells 

 giving rise to mucilage may under different conditions develop 

 volatile oil. In a general way it may be said that the secretory 

 receptacles resemble those containing mucilage, both as to the 

 manner in which they originate in a plant and the physical char- 

 acters of the secretion. Indeed, they may be closely related to 

 the mucilages in that they may contain a large proportion of gum, 

 or the proportion of oleo-resin and gum may be reversed. 



In the examination of technical products, and especially in 

 taxonomic work, it is very important to note not only the chemical 

 character of the secretions but also the fact whether the cells are 

 isolated or whether they form canals, or whether the secretory 

 receptacle is only a cavity. The following facts may be given in 

 reference to the four principal types of secretory receptacles: 



i. Secretory cells are distinct cells which may be quite dis- 

 tinct from, or may show more or less resemblance to, their 

 neighboring cells, except that they contain oil or resin. They 



