GROWTH AND WORK OF PLANTS 



54. Origin of the tissues of the root. This can be studied 

 in a longitudinal section of a young root including the tip. The 

 epidermis is the outer layer of cells. Towards the root tip the 

 rows of epidermal cells converge on a curve and meet near the 



P'o 



middle in a tissue of 

 cells rich in protoplasm 

 and with thin walls (the 

 meristem, a group of 

 growing cells at the end 

 of roots and stems). The 

 cortex lies just inside of 

 the epidermis and con- 

 sists of several rows of 

 cells on each side. In- 

 side of the cortex is 

 the central cylinder. By 

 consulting fig. 37 the 

 position and limits of 

 these tissues can be seen. 

 The meristem is the tis- 

 sue from which the oth- 

 ers arise. Its cells divide 

 and the older ones pass 



Lengthwise section (somewhat diagrammatic) through . . , . . , 



root tip of Indian corn, w, root cap; *, younger part of baCK into epidermis COr- 

 cap; z, dead cells separating from cap; s, growing point; . 



o, epidermis; p' t intermediate layer between epidermis and tCX and Central Cylinder. 

 central cylinder; p, central cylinder, in which the fibro- ,. 



vascular bundles arise. After Wiesner. In the Central Cylinder 



there is a great variety of cells. In the meristem where these cells 

 arise they are all alike, but as they age and pass over into the differ- 

 ent tissues they take on the special forms which make them suit- 

 able for their special kind of work. This is an interesting and 

 important change, since economy and the highest utility are gained 

 in this division of labor and specialization among the working cells 

 of the root. In a similar way the specialized cells of stems, leaves 

 and flowers arise from a meristem of simple undifferentiated cells. 

 The plant body may thus be compared to a highly organized and 

 developed community of individuals, each with its special work to 

 do, and all working together for the common good. 



