Plant Qrowth'Suhstances 



also be useful in grafting, thus being a refinement on the use 

 of dung. The work of Pearse (1936-7) suggests that spraying 

 may be in some cases at least as effective as lanolin smears. 



Cooper (1935), who applied a i : 2000 lanolin paste of 

 indole-acetic acid to a scraped surface at the tops of cuttings, 

 was able to induce formation of roots on leafless lemon 

 cuttings, which do not ordinarily form roots. He described 

 his experience as "very encouraging", and his 1936 paper gives 

 additional results with cuttings difficult to root. 



Evenari and Konis (1938, D) whose work is mentioned at 

 length on p. 52, repeat (in agreement with other authors) that 

 there is no general method of applying indole-acetic acid to 

 suit all cases. They point out that a lanolin preparation 

 applied to leafed cuttings may vitiate root-formation, by 

 preventing the intake of water. A related suggestion has been 

 put forward by Jackson (1938), namely, that failures to secure 

 rooting with winter cuttings after treatment with synthetic 

 growth-substances (in solution) may be due to imperfect 

 absorption by the leafless cuttings. 



Grace (1937, C) has also obtained excellent root-pro- 

 duction on woody cuttings, by dipping the bases of bunches 

 of 50 into a dust bearing o-i per cent, of growth substance by 

 weight, shaking off the excess dust, and planting immediately. 

 This technique should be very valuable, and appears to be 

 coming into general use. 



The substances tried by Grace in his very promising study 

 included indolyl-acetic, -propionic, -butyric, and a-naphthyl- 

 acetic acids, and some salts and mixtures of these. A few 

 additional details of this procedure are given in the next 

 two chapters (pp. 37, 42, 46). 



Pearse (1936-7) has examined the effects of occasional 

 and repeated spraying with solutions of phenyl-acetic and 

 indole-butyric acids, having investigated the action of 

 phenyl-acetic acid at greater length than any other worker. 

 Epinasty of leaves of young tomato plants was clearly visible 

 within thirty minutes of spraying with a o-i per cent, solution 

 of phenyl-acetic acid, which could also cause the production 

 of roots from the stem. 



32 



