Stimulation of Root Growth in Cuttings 129 



of certain toxic or inhibitory products of catabolism. If this is true it 

 strengthens the beUef of the writer that one of perhaps several causes 

 of rest is the accumulation of inhibiting by-products of catabolism, not 

 the accumulation of products of anabolism as suggested by Howard 

 (1915 b). These inhibiting substances may be similar in nature to the 

 "staling" substances produced by fungi as reported by Balls (1908), 

 or to the toxic excreta from roots which have been under investigation 

 by the men of the Bureau of Soils at Washington. 



Other experiments on the rest period of plants, on organic nutrition 

 of cuttings, and on this method of injection of organic and other sub- 

 stances, are being conducted, and therefore further data and discussion 

 regarding these topics are reserved until later. 



PART III. GENERAL DISCUSSION WITH REFERENCE TO PRACTICES 

 , COMMONLY FOLLOWED BY GREENHOUSE AND NURSERY MEN 



' In the propagation of plants by cuttings, certain general practices are 

 observed by the majority of workers. The reasons given for such practices 

 may vary widely with the individual growers. Furthermore, many of 

 those most commonly given might be termed popular reasons, and have 

 but very little scientific foundation. In some cases the real significance 

 of the practices is recognized, but in many others the governing principles 

 are apparently very poorly understood. The explanation for some of 

 these practices, in so far as the present investigation has a bearing on 

 them, are here briefly discussed. 



It is usually recognized that good aeration is necessary, and for this 

 reason a very porous medium is provided in which to start the cuttings. 

 Sand is perhaps the commonest medium employed. It is generally 

 agreed also that the medium must be well drained. This allows for 

 better aeration, tho many persons think that water as such is directly 

 injurious to the cuttings and may enter into and rot the twigs. - Cuttings 

 are sometimes started directly in water, in which case the water is held 

 in shallow pans. These,~of course, serve to give better aeration than 

 deeper dishes would afford. In the case of cuttings that have been started 

 in unglazed earthenware pots it has often been noted that those placed 

 near the edge of the pot root better than those near the center. Bailey 

 (1913:50) offers the explanation that the temperature is higher in that 

 region. As an actual fact, however, the temperature near the edge of 



