458 JOUENAL OF THE EOYAL HORTICULTURAL SOCIETY. 



exuberant callus may be slow in forming roots or refuse to do so 

 until the further application of the wound-stimulus by paring of the 

 callus. Here in the leaf it is the new shoot-formation that is retarded. 

 ^Yhy exactly this should be is another problem of propagation of which 

 we await the solution. Stimulus of callus-paring operates in hastening 

 if the callus be large, but that does not seem to meet the whole case. 

 There is, indeed, evidence that the quality of food-material may be an 

 influential factor, and that possibly an acid state of the plastic material 

 may be a requisite for shoot-formation in the circumstances. If 

 research should prove that quality of pabulum is an efficacious stimulus 

 the importance of the discovery from the practical gardening stand- 

 point would be great, and its bearings would extend beyond the 

 immediate matter of propagation by leaf -cuttings. 



From the standpoint of practical gardening the time at which a 

 cutting is taken is a matter of considerable moment in many cases. 

 In the outlook my thesis compels me to take, it bulks less largely 

 because the colonial organization of the plant lends itself sO' readily to 

 adjustment to artificial treatment and stimulus, that I might say, not 

 only that all plants can be propagated by cuttings, but, also, with 

 perhaps a large reservation, that most plants can be propagated at 

 any period under right conditions — that is to say, conditions which 

 secure that the turgescence and activity of the formative cells is 

 adequately preserved while the stimulus to growth is applied. The 

 risk in selection of a not favourable period is correlated with the 

 condition of the food-supply, the conversion of which means, prob- 

 ably, delay in striking, with the attendant danger of wilting. 



The environmental conditions necessary for striking cuttings are 

 those which govern vegetative growth generally — air, heat, and water 

 in adequate amount must be present in the soil and atmosphere — and 

 they are determinant in difficult cases. 



The use of sand, fibre, and like materials as a soil is a convention 

 that makes for aeration of the sunk portion o'f the cutting, and if the 

 relation is properly understood the evil resulting from plunging the 

 cutting too deeply is explained — the cut ends of cuttings deep in the 

 soil rot because of want of air. A canon of practice is — the sunk end 

 should go no deeper than suffices to maintain the cutting steady in 

 the soil. 



The striking of cuttings in frames in the shade means conformity 

 with the requirements of adequate temperature and moisture. 



For many plants which strike readily no special preparations are 

 necessary for securing rooted cuttings. Due attention to watering 

 brings success. But there are difficult subjects for which the balance 

 in respect of aeration, temperature, and moisture must be nicely 

 adjusted, and for which in particular heat must be used as a stimulus. 



At Edinburgh we have been so successful in striking every plant 

 we have tried that a brief description of our methods may be of some 

 value tO' practical gardeners. It is this success which begets denial of 

 the statement of my text. 



