iqiq] 



WA TERM A N—ROO T SYS TEMS 



45 



most likely to be the controlling one, some experiments were carried 

 on in the endeavor to clear up this point if possible, and to indicate 

 the nature of the chemicals producing the different results. 



Experiments with plants in situ. — The first question. to be 

 settled was, can root extension be stimulated by the presentation of 

 nutrient material either to the root tips or along the more mature 

 roots ? This was investigated by diffusing Knop's solution from 

 porous cylindrical cups (old atmometer cups in this case) which had 

 been buried in the sand near the roots of growing plants. The cups 



Fig. 17. — P. pumila, 3 months' seedlings grown in pots: a, irrigated with rain 

 water; b, with Knop's solution; c, grown in rotted barnyard naanure and humus. 



were located at a distance of 5-10 cm. from large lateral roots near 

 a portion of the root practically without secondary laterals. The 

 cups were filled about 3 times a week with 0.6 Knop's solution and 

 were dug up after 2 months. In every case there was a marked 

 development of laterals in the zone of diffusion of the solution. 

 This was tried with Prunus pumila and with Thuja occidentalis 

 (figs. 15, 16). The contrast between the old bunched roots and 

 the new slender ones is striking. Controls with distilled water 

 showed no abnormal development. 



