22 



BOTANY. 



38. This tissue is the least difEentiated of all the tissues, 

 and often differs but little from Rudimentary Tissue 

 {Meristem). It makes up the whole of the substance of 

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

 the essential portions of the assimilative (green), vegeta- 

 tive (growing), and reproductive parts. 



Practical Studies. — [a) Make very thin cross and longitudinal sec- 

 tions of a green stem of Indian corn. After excluding the woody 

 bundles, the whole of the central part of the stem is soft tissue. 



(6) Make similar sections of the central part of the stem of the cul- 

 tivated geranium. 



(c) Make a very thin cross-section of an apple-leaf: the green cells 

 are of soft tissue. 



{d) Mount a whole moss-leaf: it is entirely composed of soft tissue, 

 although in its rudimentary midrib the cells have elongated, as if 

 foreshadowing the higher tissues. 



(e) Mount several threads of Pond Scum: the whole plant is here 

 composed of soft tissue. 



39. Thick-angled Tissue (CoUencJiyma). — The cells of 



this tissue are elongated, 

 usually prismatic, and their 

 transverse walls are most fre- 

 quently horizontal, rarely in- 

 clined. The walls are greatly 

 thickened along their longi- 

 tudinal angles, while the re- 

 maining parts are thin (Fig. 

 13). "Wet specimens show by 

 transmitted light a charac- 

 teristic bluish-white lustre, 

 which is best seen in cross- 

 sections. The cells contain 

 chlorophyll, and for some 



time retain the power of fission. Without question this 



Fig. 13.— Cross-section of thick- 

 angled tissue (cl) of Begonia peti- 

 ole, showing the thickened angles, 

 e, epidermis ; cW, chloroplasts. 

 Magnified 550 times. 



