CELLULAR ANATOMY OF THE ROOT TIP 



143 



known to reach a depth ot" (30 feet. Plants with tlie Alfalfa type 

 of root system are not only drought resistant, but also loosen the 

 subsoil, which is thereby put in better condition for those plants 

 with roots less able to penetrate a hard subsoil. 



Root Structure ^ 



As the student already knows, plant organs consist of tissues, 

 each of which on account of the peculiar structure of its cells is 

 especially adapted to do a certain kind of work. 

 In roots there are tissues to perform the following 

 functions: (1) protection; (2) growth; (3) absorp- 

 tion; (4) conduction; and (5) strengthening. Root 

 tips show on their surface rather distinct regions, 

 which differ in color, texture, or some other feature 

 that can be seen without a microscope. Often, but 

 not always, the small protective cap, which is the 

 actual end of the root, can be identified by its 

 brownish color. The smooth whitish zone, which is 

 usually a conspicuous region of the tip, is where 

 cell multiplication and growth are most prominent. 

 Just back of this is the absorptive zone, bearing 

 numerous root hairs which are more conspicuous 

 when grown in moist air or moss where there are no 

 soil particles to influence their shape. {Fig. 127.) 

 Back of the absorptive region, where protective and 

 strengthening tissues are becoming prominent, the 

 root is firmer in texture and darker in color; and 

 these features become more prominent with age, as is well dem- 

 onstrated in shrubs and trees where the older parts of roots are 

 w^oody and covered with thick bark. 



Cellular Anatomy of the Root Tip. — If with the aid of a micro- 

 scope a lengthwise section through a root tip is studied, more may 

 be learned about the character of the different tissues. {Fig. 128.) 

 The root cap now appears as a well defined structure, consisting 

 of many cells loosely joined into a covering, which is thickest 

 directly over the end of the root. Next to the root cap is the 

 zone of cells active in division and constituting meristematic tissue. 

 Back of this is the growth zone, in which the chief activitj^ is cell 

 enlargement to which the elongation of the root is due. Other 



