24 



VEGETABLE PHYSIOLOGY. 



[LESSON 8. 



tie, so much so, that the least touch will produce 

 a fracture. 



144. The bark of trees is a source fruitful in 

 raphides ; they are abundantly found not only 

 in the Locust (as we have seen), but in the 

 Hickory, Apple, Pear, &c. 



145. It has been remarked that the testa 

 (shell) of many seeds contain them, and a 

 figure is given (Fig. 35) of the testa of the seed 



raphides. 



LESSON VIII. 



SCLEROGEN, OR LIGNINE. 



146. This word comes from the Greek skleros, hard, and is ap- 

 plied to certain depositions found in the interior of cells. It is also 

 called Lignine, or woody fibre ; it is supposed to be a modified form 

 of cellulose. 



147. The albumen of the fruit of a Palm (Phytelephas macro 

 carpa], hardened by this peculiar deposition, forms not only a most 

 beautiful object for the microscope, but it has become an important 

 article of commerce ; handles for canes and umbrellas are turned out 

 of this valuable substance, known as the nut, or vegetable Ivory ; 

 pipe bowls, and a variety of articles are fashioned out of it. 



148. For a few months after it is gathered, it remains so soft 

 that it DC ay be easily cut in thin sections with a penknife, but expo- 

 sure to the atmosphere inspissates it, and it becomes so remarkably 

 hard that it can be turned, and highly polished in a lathe, with great 



149. A thin section, examined by the microscope, presents a 

 charming appearance (Fig. 36). The cells are all distinctly visible, 

 each one containing in its centre a vesicle composed of sclerogen, or 

 lignine ; from this vesicle a series of tubes radiate to the inner mar- 

 gin of the cell- wall but they never pass through it to an adjoining 

 cell. In the nut ivory, the tubes are of unusual size, and have a 

 knobbed termination. 



150. Those persons who eat pears and quinces, will have observed 

 that as they approach the seeds, in the centre of these fruits, their 



