Plant Qroivth'Suhstances 



wise his technique was similar to that used by the Boyce 

 Thompson Institute workers. 



As has already been suggested on pages 12-17, the artificial 

 growth-substances should be regarded only as an aid to 

 propagation, for they will not infallibly compel cuttings to 

 form roots. Doak (1939) has recommended that cuttings 

 intended to be treated with synthetic growth-substances 

 should be taken at the time of year and condition of wood 

 most likely to lead to success without any treatment. Two 

 commercial preparations were found by Johnston (1939) to 

 be of little value in the rooting of hardwood blueberry, which 

 is known to be difficult to propagate in the ordinary way. 



Pearse and Garner (1937) have applied the solution- 

 technique to accelerate root-production of soft-wood cuttings 

 of plum and pear rootstocks; immersion of the bases for 

 twelve hours in a solution containing 30 to 40 parts of 

 a-naphthyl-acetic acid per million of water markedly improved 

 rooting. With fig and blackcurrant cuttings, accelerated 

 rooting was also obtained. 



Van der Lek and Krijthe (1937) studied the effects of indole- 

 acetic acid solutions on the rooting of plum, quince, and other 

 cuttings. They used the East Mailing types A and B (plum) 

 and A, B, and C (quince). The various types of one species 

 responded differently to a given concentration of sub- 

 stance or time of treatment. These workers are the only 

 ones who have measured the actual uptake of solution (and, 

 consequently, of growth-substance) by cuttings, and it appears 

 from their account that the same dose can produce different 

 results, depending upon the species and type of plant, and 

 upon concentration of solution and time of administration. 

 It was confirmed that, in general, a relatively high concentra- 

 tion over a short period of immersion is best. This paper 

 offers several points of novelty, and is of considerable practical 

 interest. 



As an example of the variability encountered in treatment, 

 the following fairly full abstract may serve (Komisarov (1938) : 

 "Application of growth-substances to increase the rooting 

 capacity of woody species and shrubs") : 



38 



