YampoLSKY;: Sfiidy of OU palnu 135 



as well as in the fully formed air ciiambers. It appears that the orientation 

 of the radiatino tissue in the direction that is shown in Figure 54, Plate VII 

 allows for jnst sncli a niechanical process to take place namely tearing 

 along lines of least résistance. 



De Haan ('■') has also figured such cavities for the rice plant grown 

 m Java again confirming Fl^ElDENFELTS (l.c.) contention. The septa however 

 are much thiinier, tearing resulting in establishing freer communication 

 between lacunae and consequently fewer lacunae. The cells shown by 

 DE Haan give évidence of tearing. 



The very youngest of roots in seedlings with only one leaf unfolded, 

 develop thèse lacunae and no single root of the countless that hâve been 

 examined from a very large number of plants in ail stages of growth shov^ed 

 other than the structure described above. It must be assumed then that in 

 Elaeis that is the normal condition associated with definite physiological 

 functions. Thèse lacunae are présent in roots that hâve produced no 

 pneumathodes. 



Secondary roots- 



Two kinds of secondary roots are produced from the larger roots — 

 the ordinary nutritive root and the modified root structure, the pneuma- 

 thode. Both arise endogenously so that their initial stages are the same. 

 The former develops in the manner indicated for the other roots — the 

 latter undergoes modifications which enables it to perform its spécial 

 functions. To this modified root we shall return for a more detailed 

 considération. 



The further one goes from the growing point of the root the more 

 complète the differention within the root has progressed. The hypodermis 

 has become a rigid structure, the cells of the epidermis hâve begun to 

 degenerate and they ultimately slough off, the schlerenchyma tissue has in- 

 creased. The only thin walled cells remaining unmodified are those of the septa 

 of the lacunae and small areas of the phloem. The root has taken on 

 a distinctly woody character, tough and résistant. The steps in such 

 changes shall not be discussed further in view of the voluminous litera- 

 ture on the subject. 



Advcntitious roots. 



The adventitious roots which develop in some cases for some distance 

 above the ground and those that émerge just a short distance above the 

 level of the soil and then proceed to grow into the soil are as a rule of a 

 larger diameter and they do not branch as freely as the subterranean roots. 

 They are brownish red in color with very conspicuous root caps. Occa- 

 sionally thèse roots show zones indicating the varions places of attachment 



