92 INTERCELLULAR PASSAGES. [BOOK i. 



Plantain (Musa paradisiaca) seems to prove this to be so. In 

 this plant there occurs a beautiful form of tissue, which, when 

 young, consists of strings of transparent cells, resembling 

 beads, each with a large cytoblast ; at a later period these 

 beads are so blended, that they form long continuous unin- 

 terrupted lines, referable to SchuhVs vasa expansa, and 

 very like the tissue figured by Schleiden (p. 252, f. 61), from 

 Bifrenaria atropurpurea ; at that time they are of a deep 

 brown colour ; but with age, or under the action of boiling 

 potash, they separate into short fragments evidently repre- 

 senting original cells. This tissue deserves to be very carefully 

 studied. 



SECT. VI. Of spurious elementary Organs ; such as Air Cells, 

 Receptacles of Secretion, Glands, fyc. Sfc. 



The kinds of tissue now enumerated are all that have as 

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

 however, some other internal parts, which although not 

 elementary, being themselves made up of some one or other 

 of the forms of tissue already 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 secretion; 

 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 cylin- 

 drical or spherical form. When the pressure has been very 

 uniform, as in the case of the tissue of the epidermis, and in 

 other states of cellular substance, or when elementary mucus 

 holds the tissue together completely, no spaces will exist. 

 When they do exist, they are called Intercellular passages. 

 They necessarily follow the course of the tissue, being hori- 



