30 ORGANOGRAPHY. BOOK I. 



Sect. IV. Of spuriotis elementary Organs ; such as Air Cells, 

 Receptacles of Secretion, Glands, S^c. Sfc. 



The kinds of tissue now enumerated are all that have as 

 yet been discovered in the fabric of a plant. There are, 

 however, several other internal parts, which although not 

 elementary, being themselves made up of some one or other 

 of the forms of tissue ah'eady described, nevertheless have 

 either been sometimes considered as elementary, or at least 

 are not referable to the appendages of the axis, and can be 

 treated of more conveniently in this place than elsewhere. 

 These are, 1. Intercellular passages ; 2. Receptacles of secre- 

 tion ; 3. Air cells ; 4. Raphides. 



1. Of Intercellular Passages. 



As the elementary organs are all modifications of either the 

 spherical or cylindrical figure, it must necessarily happen that 

 when they are pressed together, spaces between them will 

 remain, which will be more or less considerable in proportion 

 as the tissue preserves in a greater or less degree the cylindri- 

 cal or spherical form. Wlien the pressure has been very 

 uniform, as in the case of the tissue of the cuticle, and in many 

 states of cellular substance, no spaces will exist. When they 

 do exist, they are called Intercellular passages {meatus or ductus 

 intercellulares, canaux entrecellulaires). They necessarily follow 

 the course of the tissue, being horizontal, vertical, or oblique, 

 according to the direction of tlie angles of the tissue by which 

 they are formed. Their size varies according to the size of 

 the tissue and the quantity of sap. In plants of a dry charac- 

 ter, they are frequently so small as to be scarcely discoverable; 

 while in succulent plants they are so large as to approach the 

 size of cells, as in the stem of Tropreolum majus. (Plate II. 

 fig. 14.) They are remarkably large in the horizontal parti- 

 tions which separate the air cells of water plants. In I^inino- 

 charis Plumieri they exist in the form of,litde holes at every 

 angle of the hexagons of which the partitions in that plant 

 consist ; and are, no doubt, there intended as a beautiful con- 



