CELLS VESSELS. 



Fig. 4. 



VESICLES. 



12. The form of these cells varies very much : 

 sometimes they are spherical or octa'gonal, at other 

 times flat or very much elongated, and tapered at 

 their extremities like spindles (jig- 4) ; in the latter 

 case they are often designated under the name of 

 clostres. Their surface frequently presents rays or 

 points which resemble pores, but in reality these vesi- 

 cles are completely closed, and are without openings 

 or orifices ; their parietes are naturally transparent, 

 and almost colourless; but ordinarily these cells con- 

 tain granules which are deposited on their internal 

 surface, and, when these corpuscles (little bodies) are green, 

 brown, red, &c., their parietes appear to be coloured in the same 

 manner. The colour of different parts of plants depends upon 

 this circumstance. 



13. The cellules (little cells) of the cellular tissue often have 

 between them empty spaces of more or less extent, called inter- 

 cellular mca'tus, or inter-cellular pores, or passages : these 

 cavities, which are of irregular form, are very important, as we 

 shall see in the sequel. 



Of Vessels. 



14. The vessels of plants are generally cylindrical 

 tubes, which sometimes resemble excessively elon- 

 gated cells (Jig. 5). They differ very much in their 

 structure, and they are divided into tracheas, false tra- 

 chese, punctuated or dotted vessels, moniliform vessels, 

 reticular vessels, mixed vessels and proper vessels. 



15. Trachea. We give the name of trachese to 



tubes, which closely resemble the 

 tracheae of insects, for, like them, 

 they are formed of a thread 

 spirally folded (fig. 6). This thread, which 

 is silvery white, is very elastic and easily 

 unrolled ; and if we carefully break a leaf 

 of a rose tree, or dog- wood, for example, we 



Fig. 5. 



VESSEL. 



a b cd e f g 



Fig. 6. TRACHEA. 



Explanation af Fig 4. Clostres or fusiform cells of wood, magnified. 



Explanation of Fig. 5. A punctuated or dotted vessel, magnified. 



Explanation of Fig. 6. Vertical section of a stem, showing the cellular 

 tissue of which the epidermis is composed (a) ; the cellular tissue of the 

 bark (&) ; the clostres of the fibre of the wood (c) ; a punctuated vessel (d) J 

 n rayed vessel (e) ; a tracheae (/) ; and soft cellular tissue (g). 



12. What are clostres? 



13. What are inter-cellular passages ? 



14. How are the vessels of plants divided? 



15. What are tra'cheae ? (Tracheae, the plural of trachea, pronounced 

 tra'-ke-ah wind-pipe.) 



