16 



BOTANY. 



most important and the most variable. It is composed of 

 cells whose walls are thin, colorless, or nearly so, and trans- 

 parent; in outline they may be rounded, cubical, polyhe- 

 dral, prismatic, cylindrical, tabular, stellate, and of many 

 other forms. "When the cells are bounded by plane sur- 

 faces, generally, but not always, the end planes lie at right 

 angles to the longer axis of the cells. 



37. This tissue makes up the whole of the substance of 

 many of the lower plants, while in the higher it composes 



the essential portions of the as- 

 similative (green), vegetative 

 (growing), and reproductive 

 parts. 



38. Thick - angeled Tissue 

 {GoUenchyma). — The cells of 

 this tissue are elongated, usu- 

 ally prismatic, and their trans- 

 verse walls are most frequent- 

 ly horizontal, rarely inclined. 

 The walls are greatly thick- 

 ened along their longitudinal 

 Fig. 8. —Cross-section of thick-angled auffles, while the remaining 



tissue (cD of Begonia petiole, showing S ' o 



the thickened angles, e, epidermis; y-o-fg m-f> thin (V\a 8^ Thp 



cftj, chlorophyll-bodies. Magnified 550 P^rts are mm (,rig. «;. J.ne 

 *'"®^- cells contain chlorophyll, and 



retain the power of fission. Wet specimens show by trans- 

 mitted light a characteristic bluish- white lustre, which is 

 best seen in cross-sections. 



39. Thick-angled tissue is found beneath the epidermis 

 of most flowering plants (and some ferns), usually as a mass 

 of considerable thickness, and is doubtless developed from 

 soft tissue for the purpose of giving support and strength 

 to the epidermis. 



