LINUM USITATISSIMUM 



405 



produced by this cambium, and the cambium of the hypocotyl 

 proper, form a new plant axis which is almost straight. 



Fig. zo6. Longisection of hypocotyl showing development of adventitious bud after 

 plant has been severed below cotyledons : en, endodermis. (After Crooks.) 



Adventitious Roots. — When seedlings six to ten days old are 

 severed at the mid-hypocotyledonary region, and the upper part 

 of the axis is set in moist soil with the cotyledons just above the 

 soil level, the elongation of the hypocotyl lifts the cotyledons from 

 I to 3 cm. above the ground level, depending upon the age of the 

 plant at the time of cutting. Cuttings so treated produce from two 

 to five adventitious roots at the lower limits of the hypocotyl, even 

 when it is severed very close to the cotyledons. Cuttings of the 

 epicotyledonary internodes, treated in a similar manner, also pro- 

 duce adventitious roots. 



In the hypocotyl, the roots are usually initiated by a general 

 activation of the cells of the V-shaped rays of parenchymatous 



